Toyota Hybrid System Overview.pdf

TOYOTA Hybrid System - Course 071 1-1
Prius is a Latin word meaning to go before." Toyota chose this name
because the Prius vehicle is the predecessor of cars to come. Rapid
population growth and economic development in recent decades have
resulted in a sharp increase in fossil fuel consumption on a global
scale. Faced with the challenges to create an earth−friendly vehicle,
Toyota has produced the world’s first mass produced hybrid
automobile.
The hybrid system is the wave of the future, and now there are more
incentives to purchase one. Owners of the Prius, or any other hybrid
gas−and−electric vehicle, may be eligible for a federal income tax
deduction. According to the Internal Revenue Service, hybrid vehicles
qualify for a long−standing tax deduction that applies to vehicles
powered by clean−burning fuels. The policy allows a one−time
deduction, which can be claimed by the consumer for the year the car
was first put in use.
In its simplest form, a hybrid system combines the best operating
characteristics of an internal combustion engine and an electric motor.
More sophisticated hybrid systems, such the Toyota Hybrid System,
recover energy otherwise lost to heat in the brakes and use it to
supplement the power of its fuel−burning engine. These sophisticated
techniques allow the Toyota Hybrid System to achieve superior fuel
efficiency and a massive reduction in CO2.
When the Prius was first released, it was selected as the world’s
best−engineered passenger car for 2001. The car was chosen because it
is the first hybrid vehicle that seats four to five people plus their
luggage, and it is one of the most economical and environmentally
friendly vehicles available. Then in 2004, the second generation Prius
won the prestigious Motor Trend Car of the Year award and
best−engineered vehicle of 2004.
Section 1
Hybrid System Overview
Overview
[click here repair_cars]

Section 1
1-2 TOYOTA Technical Training
The Toyota Hybrid System (THS) powertrain in the original Prius and
the Toyota Hybrid System II (THS−II) powertrain in the second
generation Prius both provide impressive EPA fuel economy numbers
and extremely clean emissions:
THS (2001−2003 Prius) THS−II (2004 & Later)
City: 52 mpg City: 60 mpg
Highway: 45 mpg Highway: 51 mpg
SULEV AT−PZEV
• SULEV standards are about 75% more stringent than ULEV and
nearly 90% cleaner than LEV for smog forming exhaust gases.
• SULEV vehicles will emit less than a single pound of hydrocarbons
during 100,000 miles of driving (about the same as spilling a pint of
gasoline).
• AT−PZEV vehicles use advanced technology capable of producing
zero emissions during at least part of the vehicle’s drive cycle.
CARB Emission
Ratings
Figure 1.1 T072f101c

Hybrid System
Components
The main components of the hybrid system are:
• IC Engine
• Motor Generator 1 (MG1)
• Motor Generator 2 (MG2)
• Planetary Gear Set
• Inverter
• HV Battery
• HV ECU
Hybrid System

Section 1
The 1NZ−FXE 1.5−liter gasoline engine employs VVT−i variable valve
timing and ETCS−i electronic throttle control.
1NZ-FXE
Figure 1.3 T071f103p
IC Engine

Motor Generator 1 (MG1) operates as the control element for the power
splitting planetary gear set. It recharges the HV battery and also
supplies electrical power to drive Motor Generator 2 (MG2). MG1
effectively controls the continuously variable transmission function of
the transaxle and operates as the engine starter.
Motor Generator 1
(MG1)
MG1 generates electrical
power and starts the engine.
Motor Generator 1
(MG1)

Section 1
MG2 is used for motive force at low speeds and supplemental force at
high speeds. It provides power assist to the engine output as needed
and helps the vehicle achieve excellent dynamic performance. It also
functions as a generator during regenerative braking.
Motor Generator 2
(MG2)
MG2 drives the vehicle.
Motor Generator 2
(MG2)

The planetary gear unit is a power splitting device. MG1 is connected
to the sun gear, MG2 is connected to the ring gear and the engine
output shaft is connected to the planetary carrier. These components
are used to combine power delivery from the engine and MG2, and to
recover energy to the HV battery.
Planetary Gear Unit
A single Planetary Gear Unit
splits the torque between
MG1, MG2, and the engine.
Planetary Gear Unit

Section 1
Current between MG1, MG2 and the HV battery is controlled by the
inverter. The inverter converts high−voltage battery DC to AC power,
and it rectifies high−voltage AC from MG1 and MG2 to recharge the
high−voltage battery.
Inverter Assembly
A device that converts the
high-voltage DC
(HV battery) into AC (MG1
and MG2) and vice versa.
Inverter

The battery stores power recovered by MG2 during regenerative
braking and power generated by MG1. The battery supplies power to
the electric motor when starting off or when additional power is
required.
THS (2001−2003 Prius) THS−II (2004 and later Prius)
38 Nickel−Metal Hydride modules 28 Nickel−Metal Hydride modules
Total voltage: 273.6V Total voltage: 201.6V
HV Battery
Supplies electric power
to MG2 during start-off,
acceleration and
uphill driving.
HV Battery

Section 1
When starting off and traveling at low speeds, MG2 provides the
primary motive force. The engine may start immediately if the HV
battery State of Charge (SOC) is low. As speed increases above 15 to 20
mph the engine will start.
When driving under normal conditions, the engine’s energy is divided
into two paths; a portion drives the wheels and a portion drives MG1 to
produce electricity. The HV ECU controls the energy distribution ratio
for maximum efficiency.
During full acceleration, power generated by the engine and MG1 is
supplemented by power from the HV battery. Engine torque combined
with MG2 torque delivers the power required to accelerate the vehicle.
During deceleration or braking, the wheels drive MG2. MG2 acts as a
generator for regenerative power recovery. The recovered energy from
braking is stored in the HV battery pack.
The hybrid system uses various modes to achieve the most efficient
operation in response to the driving conditions. The following graphics
review each of these modes.
Hybrid System
Control Modes
Hybrid Control
Modes

If the vehicle is fully charged and it not moving, the engine may stop.
The engine will start up automatically if the HV battery needs
charging. Also, if MAX A/C is selected on a 2001 – 2003 Prius, the
engine will run continuously due to the engine driven compressor. The
2004 & later Prius use an electric compressor.
Stopped
The engine may stop when
the vehicle is not moving
and the HV battery is
fully charged.
Stopped

Section 1
When starting out under light load and light throttle, only MG2 turns
to provide power. The engine does not run and the vehicle runs on
electric power only. MG1 rotates backwards and just idles; it does not
generate electricity.
Starting Out
The electric power supply
from the HV battery to MG2
provides force to drive
the wheels.
Starting Out

During normal low−speed driving (15 – 40mph), the engine runs and
provides power. MG2 turns and runs as a motor and provides an
electric assist. MG1 is turned in the same direction by the engine as a
generator and provides electricity for MG2.
Normal Driving
While the engine drives
the wheels via the planetary
gears, MG1 is driven via the
planetary gears to supply
electricity to MG2.
Normal Driving

Section 1
For maximum acceleration or speed (over 100mph), electric drive
power from MG2 supplements engine power. The HV battery provides
electricity to MG2. MG1 also receives electrical power from the HV
battery and turns in the reverse direction to create an overdrive ratio
for maximum speed.
Full Throttle
Acceleration and
High Speed Cruise
MG2 supplements engine
power for maximum
acceleration or speed.
Full Throttle
Acceleration and
High Speed Cruise

As soon as the driver releases the accelerator pedal, MG2 becomes a
generator. MG2 is turned by the drive wheels and generates electricity
to recharge the HV battery. This process is called Regenerative
Braking. As the vehicle decelerates, the engine stops running and MG1
turns backwards to maintain the gear ratio.
When the brake pedal is depressed, most initial braking force comes
from Regenerative Braking and the force required to turn MG2 as a
generator. The hydraulic brakes provide more stopping power as the
vehicle slows.
Deceleration and
Braking
When the vehicle
decelerates, kinetic energy
from the wheels is recovered
and converted in to
electrical energy and used to
recharge the HV battery
by means of MG2.
Deceleration
and Braking

Section 1
When the vehicle moves in reverse, MG2 turns in reverse as an electric
motor. The engine does not run. MG1 turns in the forward direction
and just idles; it does not generate electricity.
Reverse
MG2 rotates backwards to
move the vehicle in reverse.
The engine does not run.
Reverse

A multi display is provided on the center cluster panel as standard
equipment. The 7.0−inch LCD screen has a pressure sensitive panel for
easy function accessibility.
Energy Monitor
Fuel Consumption
Screen
Multi Display

Section 1
In addition to the conventional mechanical key function and wireless
door lock remote control function, this system provides a smart key
with a bi−directional communication function. By enabling the smart
ECU to recognize the presence of the smart key within the detection
area, this system can lock or unlock the doors, or start the hybrid
system without the use of the key, as long as the user has the smart
key in their possession.
Door Open
Using smart entry by opening
the door with smart key in
pocket. The touch sensor is
located on the back of the
door handle.
Smart Entry and
Start System

On the ’01−‘03 Prius, an ignition key is used to operate the key cylinder
(containing the ignition switch), in order to switch the power mode of
the vehicle and start the system.
On the ’04 & later Prius, a push button start system operates the
power switch by inserting a key in a key slot or by the driver keeping a
key in their possession (models with smart entry and start system).
A power mode (OFF, ACC, IG−ON, or READY) can be selected by
pressing the power switch. The indicator on this switch will tell you the
power mode, which varies depending if the brake pedal is depressed or
not while the switch is operated.
Push Button Start
(’04 & later Prius)
Hybrid System Start
Using smart start system by
pressing the Power button
with foot on brake and
key in pocket.
Hybrid System
Start
Power Mode

Section 1
Smart Cancel Switch
To cancel smart key and
smart on a ’04 & later Prius.
Simply press the smart
cancel switch under the
steering column.
Power Mode –
OFF or READY
Indicator light is OFF.

Power Mode - ACC
Indicator light is green.
Power Mode – IG-ON
Indicator light is amber.
Combination Meter

Section 1

WORKSHEET 1-1
Vehicle Year/Prod. Date Engine Transmission
Worksheet Objectives
Review this sheet as you are doing the Hybrid System Overview worksheet. Check off either category after
completing the worksheet and instructor presentation. Ask the instructor if you have questions. The Comments
section is for you to write notes on where to find the information, questions, etc.
Tools and Equipment
• Vehicle
• Repair Manual
• New Car Features
Section 1: Hybrid Overview
1. On the multi display screen, view the fuel consumption screen. What different types of information are
displayed on this screen?
2. Unlike a conventional vehicle, the Prius may or may not start the engine when the vehicle is turned ON.
What alerts the driver that the vehicle is ready to drive?
3. What is the primary motive force when starting, backing up or under light loads?

Section 1
4. While driving, what do you think happens when you shift into the “B” position?
5. When the vehicle is decelerating or braking, what kind of energy from the wheels is recovered and
converted into electrical energy to recharge the HV Battery?
6. Where is the 12V auxiliary battery located and what is its function? Can the 12V battery be jump-started?
7. How can you tell if the vehicle has smart key and smart start?
8. Does the vehicle you are working on have navigation? Does it have Bluetooth? How can you tell?
9. Where is the intake duct for the HV battery cooling system?
Section 2: Driving Characteristics
1. Make sure the parking brake is engaged. Will the vehicle start in neutral?
2. When the vehicle begins to move forward after the release of the parking brake and brake pedal, what
power source is being used to move the vehicle?

3. On a 2004 and later Prius, how do you start the vehicle (READY light ON) with the Power button? With and
without smart key?
4. What is unique about the steering system?
5. The engine may turn OFF periodically. List two conditions that will cause the engine to turn back ON.
Return all cars to the original state and return to the classroom.

Section 1

SELF-ASSESSMENT 1-1
Name: Date:
Self-assessment Objectives
Review this sheet as you are doing the Inclination Sensor Reset worksheet. Check off either category after
I have questions I know I can
Topic Comment
Locate power button.
Access the READY light.
Use smart key & smart start.
Locate the 12V battery.
Locate the Navigation & Bluetooth functions.
TOYOTA HYBRID SYSTEM

Section 1

The Toyota hybrid system has two drive sources: the gasoline engine
and the electric motor. The hybrid control system selects the best
combination of those two power sources depending on driving
conditions.
• The ’01−’03 Prius uses THS (Toyota Hybrid System).
• The ’04 & later Prius uses THS−II, which carries over the same
basic concepts as the previous model but offers improvements to
MG1 and MG2, the battery and engine.
Hybrid System
Components
Section 2
Hybrid System Operation
Overview

Section 2
Hybrid Control
System Diagram
Hybrid system components include:
• Hybrid Transaxle, consisting of MG1, MG2 and a Planetary Gear Unit
• 1NZ−FXE engine
• Inverter Assembly containing an inverter, a boost converter, a
DC−DC converter, and an A/C inverter
• HV ECU, which gathers information from the sensors and sends
calculated results to the ECM, inverter assembly, battery ECU and
skid control ECU to control the hybrid system
• Shift Position Sensor
• Accelerator Pedal Position Sensor, which converts accelerator angle
into an electrical signal
• Skid Control ECU that controls regenerative braking
• ECM
• HV Battery
• Battery ECU, which monitors the charging condition of the HV
battery and controls cooling fan operation
• Service Plug, which shuts off the circuit
• The SMR (System Main Relay) that connects and disconnects the
high−voltage power circuit
• Auxiliary Battery, which stores 12V DC for the vehicle’s control
systems
Hybrid System
Components

Incorrectly performed hybrid system repairs could cause electrical
shock, battery leakage or even an explosion. Be sure to perform the
following safety procedures whenever servicing the hybrid vehicle’s
high−voltage system or hybrid control system:
• Remove the key from the ignition. If the vehicle is equipped with
smart key, turn the smart key system off.
• Disconnect the negative (−) terminal of the auxiliary battery.
• Wear insulated gloves.
• Remove service plug and put it in your pocket.
• Do not make any repairs for five minutes.
If the key cannot be removed from the key slot (for instance, because of
body damage during an accident) be sure to perform the following
procedures:
• Disconnect the auxiliary battery.
• Remove the HEV fuse (20A yellow fuse in the engine compartment
junction block.) When in doubt, pull all four fuses in the fuse block.
High−voltage insulated gloves can be ordered from the Toyota SPX/OTC
SST catalog under part numbers:
Small gloves – 00002−03100−S
Medium gloves – 00002−03200−M
Large gloves – 00002−03300−L
To check the integrity of the glove’s surface, blow air into the glove and
fold the base of the glove over to seal the air inside. Then, slowly roll
the base of the glove towards the fingers.
• If the glove holds pressure, its insulating properties are intact.
• If there is an air leak, high−voltage electricity can find its way back
through that same hole and into your body! Discard the glove(s)
and start over until you have a pair of gloves that can fully protect
you from the vehicle’s high−voltage circuits.
After disabling the vehicle, power is maintained for 90 seconds in the
SRS system and for five minutes in the high−voltage electrical system.
If any of the disabling steps above cannot be performed, proceed with
caution as there is no assurance that the high−voltage electrical
system, SRS or fuel pumps are disabled. Never cut orange high−voltage
power cables or open high−voltage components.
Safety Procedures
NOTE
WARNING

Section 2
Due to circuit resistance, it takes at least five minutes before
high−voltage is discharged from the inverter circuit. Even after five
minutes have passed, the following safety precautions should be
observed:
• Before touching an orange high−voltage cable, or any other cable
that you cannot identify, use the tester to confirm that the voltage
in the cable is 12V or less.
• After removing the service plug, cover the plug connector using
rubber or vinyl tape.
• After removing a high−voltage cable, be sure to cover the terminal
using rubber or vinyl tape.
• Use insulated tools when available.
• Do not leave tools or parts (bolts, nuts, etc.) inside the cabin.
• Do not wear metallic objects. (A metallic object may cause a
short−circuit.)
Many fire departments and police stations have been trained to safely
remove hybrid vehicles from water in case of an emergency. Always call
your local fire department in this situation.
To safely handle a Prius that is fully or partially submerged in water,
disable the high−voltage electrical system and SRS airbags. Remove the
vehicle from the water. Drain the water from the vehicle if possible.
Then, follow the extrication and vehicle disable procedures below:
• Immobilize the vehicle.
• Chock the wheels and set the parking brake.
• Remove the key from the key slot.
• If equipped with smart key, use the smart cancel switch underneath
the steering column to disable the system.
• Keep the electronic key at least 16 feet (5 meters) away from
the vehicle.
• Disconnect the 12V auxiliary battery.
• Remove the HEV fuse in the engine compartment. When in doubt,
pull all four fuses in the fuse block.
WARNING
Submerged
Vehicle Safety

Service Plug
(’01-’03 Prius)
Service Plug
The hybrid transaxle contains:
• Motor Generator 1 (MG1) that generates electrical power.
• Motor Generator 2 (MG2) that drives the vehicle.
• A planetary gear unit that provides continuously variable gear
ratios and serves as a power splitting device.
• A reduction unit consisting of a silent chain, counter gears and final
gears.
• A standard 2−pinion differential
The ‘01−‘03 Prius uses the P111 hybrid transaxle.
The ‘04 & later Prius uses the P112 hybrid transaxle. The P112 is
based on the P111, but offers a higher RPM range, V−shaped
permanent magnets in the rotor of MG2, and a newly designed
over−modulation control system.
Hybrid Transaxle

Section 2
Hybrid Transaxle
The transaxle damper uses a spring coil with low torsional
characteristics. In the ’04 & later Prius, the spring rate characteristics
of the coil spring have been reduced further to improve its vibration
absorption performance and the shape of the flywheel has been
optimized for weight reduction.
Transaxle Damper
The transaxle damper, which
transmits the drive force of
the engine to the transaxle,
contains a torque fluctuation
adsorption mechanism that
uses a dry, single plate
friction material.
Transaxle Damper

Hybrid Transaxle ’04 Model ’03 Model
Hybrid Transaxle
Specifications Transaxle Type P112 P111
Specifications
The No. of Ring Gear Teeth 78 ←
Planetary Gear The No. of Pinion Gear Teeth 23 ←
Planetary Gear
The No. of Sun Gear Teeth 30 ←
Differential Gear Ratio 4.113 3.905
Number of Links 72 74
Chain Drive Sprocket 36 39
Chain
Driven Sprocket 35 36
Counter Gear
Drive Gear 30 ←
Counter Gear
Driven Gear 44 ←
Final Gear
Drive Gear 26 ←
Final Gear
Driven Gear 75 ←
Fluid Capacity Liters (US qts Imp qts) 3 8 (4 0 3 3) 4 6 (4 9 4 0)
Fluid Capacity Liters (US qts, Imp qts) 3.8 (4.0, 3.3) 4.6 (4.9, 4.0)
Fluid Type
ATF WS or
equivalent
ATF Type T-IV
or equivalent
Fluid Ty e
equivalent or equivalent
MG1 and MG2 function as both highly efficient alternating current
synchronous generators and electric motors. MG1 and MG2 also serve
as sources of supplemental motive force that provide power assistance
to the engine as needed.
MG1 and MG2 MG1 Specifications ’04 Model ’03 Model
MG1 and MG2
Specifications Item
p
Type Permanent Magnet Motor
Function Generate, Engine Starter
Maximum Voltage [V] AC 500 AC 273.6
Cooling System Water-cooled
MG2 Specifications ’04 Model ’03 Model
Item
Type Permanent Magnet Motor
Function Generate, Engine Starter
Maximum Voltage [V] AC 500 AC 273.6
Maximum Output kW (PS) / rpm 50 (68) / 1,200 ~1,540 33 (45) / 1,040 ~ 5,600
Maximum Torque N•m (kgf•m) / rpm 400 (40.8) / 0 ~ 1,200 350 (35.7) / 0 ~ 400
Cooling System Water-cooled
MG1 & MG2
Motor Generator 1 &
Motor Generator 2

Section 2
MG1 recharges the HV battery and supplies electrical power to drive
MG2. In addition, by regulating the amount of electrical power
generated (thus varying MG1’s internal resistance and rpm), MG1
effectively controls the transaxle’s continuously variable transmission.
MG1 also serves as the engine starter.
MG2 and the engine work together to drive the wheels. The addition of
MG2’s strong torque characteristics help achieve excellent dynamic
performance, including smooth start−off and acceleration. During
regenerative braking, MG2 converts kinetic energy into electrical
energy, which is then stored in the HV battery.
Towing a damaged Prius with its front wheels on the ground may cause
MG2 to generate electricity. If that happens, the electrical insulation
could leak and cause a fire. Always tow the vehicle with the front
wheels off of the ground or on a flat bed.
The planetary gear unit is used as a power splitting device. The sun
gear is connected to MG1, the ring gear is connected to MG2, and the
planetary carrier is connected to the engine output shaft. The motive
force is transmitted from the chain drive sprocket to the reduction unit
via a silent chain.
Item Connection
Sun Gear MG1
Ring Gear MG2
Carrier Engine Output Shaft
MG1 Description
MG2 Description
NOTE
Planetary Gear Unit
Planetary Gear
Connection
Figure 2.8 T072f035

The reduction unit consists of the silent chain, counter gears and final
gears. A silent chain with a small pitch width ensures quiet operation.
The overall length has been reduced in contrast to the gear−driven
mechanism. The counter gear and final gear teeth have been processed
through high−precision honing and their tooth flanks have been
optimized to ensure extremely quiet operation.
Reduction Unit
The final gears have been
optimized to reduce the
distance between the
engine’s center shaft and the
differential shaft, resulting in
a more compact
transmission.
Reduction Unit

Section 2
When three−phase alternating current is passed through the windings
of the stator coil, a rotating magnetic field is created. When the
rotation of this magnetic field is properly timed in relationship to the
rotor, the magnetic field pulls the permanent magnets housed inside
the rotor in a circle, causing the rotor to turn and creating the motor’s
torque. The generated torque is proportionate to the amount of current
passing through the stator coils and the rotational speed is controlled
by the frequency of the three−phase alternating current.
A high level of torque can be generated efficiently at all speeds by
properly controlling the rotating magnetic field and the angles of the
rotor magnets.
On the ’04 & later Prius the built−in permanent magnets have been
changed to a V−shaped structure to improve both power output and
torque.
Permanent
Magnet Motor
Permanent
Magnet Motor

Permanent Magnet
Structure
The V-shaped structure of
the magnets in the ’04 & later
model provides about
50% more power than
previous models.
This reliable and compact sensor precisely detects the magnetic pole
position, which is essential for the control of MG1 and MG2.
The sensor’s stator contains three coils. Since the rotor is oval, the gap
between the stator and the rotor varies with the rotation of the rotor.
In addition, the HV ECU uses this sensor as an rpm sensor, calculating
the amount of positional variance within a predetermined time
interval.
Speed Sensor
(Resolver) Operation
Output coils B and C are
electrically staggered
90 degrees. Because the
rotor is oval, the distance of
the gap between the stator
and the rotor varies with the
rotation of the rotor. By
passing an alternating current
through coil A, output that
corresponds to the sensor
rotor’s position is generated
by coils B and C. The
absolute position can then be
detected from the difference
between these outputs.
Figure 2.12 T071f212
Speed Sensor
(Resolver)

Section 2
Inverter Assembly
The inverter changes high−voltage direct current from the HV battery
into three−phase alternating current for MG1 and MG2. The HV ECU
controls the activation of the power transistors. In addition, the
inverter transmits information that is needed to control current, such
as the output amperage or voltage, to the HV ECU.
The inverter, MG1, and MG2, are cooled by a dedicated radiator and
coolant system that is separate from the engine coolant system. The
HV ECU controls the electric water pump for this system. In the ’04 &
later Prius, the radiator has been simplified and the space it occupies
has been optimized.
The boost converter boosts the nominal voltage of 201.6V DC that is
output by the HV battery to the maximum voltage of 500V DC. To boost
the voltage, the converter uses a boost IPM (Integrated Power Module)
with a built−in IGBT (Insulated Gate Bipolar Transistor) for switching
control, and a reactor to store the energy.
When MG1 or MG2 acts as a generator, the inverter converts the
alternating current (range of 201.6V to 500V) generated by either
motor into direct current, then the boost converter drops the voltage to
201.6V DC to charge the HV battery.
Inverter
Boost Converter

Inverter Assembly
Diagram
The vehicle’s auxiliary equipment (such as lights, audio system, A/C
cooling fan, ECUs, etc.) is powered by standard 12V DC.
On the ’01−’03 Prius, the THS generator voltage is 273.6V DC. A
converter transforms the voltage from 273.6V DC to 12V DC to
recharge the auxiliary battery.
On the ’04 and later Prius, the THS−II generator outputs a nominal
voltage of 201.6V DC. The converter transforms the voltage from
201.6V DC to 12V DC to recharge the auxiliary battery.
DC/DC Converter
System Diagram
The inverter is installed on
the underside of the inverter.
Converter

Section 2
The inverter assembly includes a separate inverter for the air
conditioning system that changes the HV battery’s nominal voltage of
201.6V DC into 201.6V AC to power the air conditioning system’s
electric inverter compressor.
A/C Inverter
A/C Inverter

A dedicated cooling system uses a water pump to cool the inverter,
MG1 and MG2. It is separate from the engine cooling system. This
cooling system activates when the power supply is switched to IG.
Cooling System
The radiator for the cooling
system is integrated with the
radiator for the engine.
The HV ECU:
• Controls MG1, MG2 and the engine based on torque demand,
regenerative brake control and the HV Battery’s State of Charge
(SOC). These factors are determined by the shift position, the
degree with which the accelerator is depressed and vehicle speed.
• The HV ECU monitors HV Battery SOC and the temperature of the
HV battery, MG1 and MG2.
• To ensure reliable circuit shutdown and protect the vehicle’s
circuits from high−voltage, the HV ECU uses three relays housed in
the System Main Relay assembly to connect and disconnect the
high−voltage circuit.
• If the HV ECU detects a malfunction in the hybrid system, it will
control the system based on the data that is stored in its memory.
Cooling System
for Inverter, MG1
and MG2
HV ECU

Section 2
A nomograph is a kind of chart that conveys the relationship between
different sets of numbers. The hybrid operation nomographs below
convey the relationship between RPM for MG1, MG2 and the engine.
Because MG1, MG2 and the engine are mechanically connected in the
Planetary Gear Set, if one of the components changes rpm, the rpm of
the other components will be affected. So in the nomograph, the rpm
values of the 3 power sources maintain a relationship in which they are
always connected by a straight line.
Hybrid Nomograph
Ready-on.
Nomographs

Hybrid Nomograph
Starting out.
Hybrid Nomograph
Engine starting.

Section 2
Hybrid Nomograph
Light acceleration
with engine.
Hybrid Nomograph
Low speed cruising.

Hybrid Nomograph
Full acceleration.
Hybrid Nomograph
High speed cruising.

Section 2
Hybrid Nomograph
Max speed.
Hybrid Nomograph
Deceleration or braking.

Hybrid Nomograph
Reverse.
Information Codes are a three−digit supplement to HV ECU DTCs.
They provide additional information and freeze frame data to help
diagnose the vehicle’s condition. These codes can be found on the
Diagnostic Tester HV ECU menu. Use the screen flow shown below to
access the codes. For a detailed description of each Information Code,
refer to the DI section of the Repair Manual.
Using Information
Codes

Section 2
Accessing
Information Codes
Follow the screen flow
to access the
Information Codes.
Figure 2.28 T071f228

TOYOTA Hybrid System - Course 071 2W1-1
WORKSHEET 2-1
Hybrid Safety
Technician Objectives
This worksheet will familiarize you with the critical safety procedures involved in working with a high-voltage
hybrid system. You will understand all safety procedures and use all safety equipment.
Tools and Equipment
• High-Voltage Gloves
• Protective Eye Wear
• Emergency Response Guide
• Repair Manual
• EWD
Section 1: In Class - Hybrid Safety
1. Fill in the blanks in the following statements about hybrid safety.
a. Always follow the directions and warnings in the and .
b. Always wear your high-voltage and protective .
c. Remove the from the 12V battery.
d. Put the in your pocket and keep it under your control at all times.
e. Wait at least minutes before inspecting any high-voltage system.
f. Always verify the with a .
2. Using the Emergency Response Guide, explain how you could disable a hybrid vehicle if the ignition key or
service plug were inaccessible?

Hybrid System Overview TOYOTA HYBRID SYSTEM
SELF-ASSESSMENT 2-1
Hybrid Safety
Name: Date:
Review this sheet as you are doing the Hybrid Safety worksheet. Check off either category after completing the
worksheet and instructor presentation. Ask the instructor if you have questions. The Comments section is for
you to write notes on where to find the information, questions, etc.
Topic Comment
Describe all safety procedures when working
with the high voltages systems.
Locate and list all safety equipment.
Access the 12V battery.
Access the high-voltage battery.
Safely pull the service plug.
Describe when the service plug needs to be
removed.

Hybrid Safety TOYOTA HYBRID SYSTEM
2W1-4 TOYOTA Technical Training

WORKSHEET 2-2
Data List Information – Test Drive
In this worksheet you will use the Diagnostic Tester to obtain and view relevant information and observe data
lists while driving the vehicle. You will then relate this information to the different components and technologies
of the hybrid system.
Tools and Equipment
• Vehicle
• Diagnostic Tester
• TIS Machine w/Tech View
Section 1 – HV ECU Data List
1. Connect the Diagnostic Tester to DLC3. Start the vehicle (READY light ON).
2. Go to HV ECU, Data List.
3. Create a User Data list with the following items:
• MG1 REV
• MG2 REV
• MG1 TORQ
• MG2 TORQ
• POWER RQST
• ENGINE SPD
• VEHICLE SPEED
Note: Remember that when REV and TORQ are the same (both + positive or both – negative) the
component is being used as a MOTOR. When REV and TORQ are different (ie. REV + & TORQ -) the
component is a GENERATOR.

Hybrid Safety TOYOTA HYBRID SYSTEM
Section 2: In Shop - Hybrid Safety
Note: Bring your safety gloves and ERG to the shop.
1. Remove the key from the vehicle and put it in your pocket. (The ‘04 and later smart key equipped vehicles
will require the smart key system to be turned OFF first.)
2. Access the 12V auxiliary battery and remove the negative terminal. This assures what?
3. Locate the Service Plug. Put on your safety gloves and protective eye wear and remove the plug. What
device or devices are integrated into the service plug assembly?
4. Re-install the service plug and allow another student to remove the plug wearing their gloves.
5. When each student has removed and re-installed the plug, use the Repair Manual, EWD, or TIS workstation
to locate the IGCT Relay or HEV fuse in the vehicle. Write the location of the relay below.
6. When would you need to remove this relay?
Return vehicle to normal condition.

Data List Information - Test Drive TOYOTA HYBRID SYSTEM
4. From a stop, lightly accelerate to 20 mph. Record the following values:
MG1 REV - MG1 TORQ -
ENGINE SPD -
5. Is MG1 being used as motor or a generator?
6. Is MG2 being used as a motor or generator?
7. Is the engine running?
8. Bring vehicle speed up to approximately 35 mph. Record the following values:
ENGINE SPD -
12. Bring vehicle speed up to approximately 45 mph. Record the following values:
ENGINE SPD -

SECTION 2 – Battery ECU Data List
1. With the Diagnostic Tester, select Battery ECU and enter the Data List.
2. Create a User Data list (use YES/NO keys to turn ON) with the following:
• BATTERY SOC
• BATT TEMP 1
• BATT TEMP 2
• BATT TEMP 3
• BATT TEMP 4
• BATT BLOCK V1
• BATT BLOCK V2
3. What is the battery SOC?
4. What is the AVG battery temperature?
5. What is the voltage of the battery blocks? V1 V2 .
6. From a standing start accelerate to 20 mph. How is the temperature changing?
7. Is SOC (State Of Charge) changing?
8. Cruise at approx 35 mph. How is the temperature changing?
9. How is the SOC changing?

10. Accelerate full throttle to approx 45 mph. How is the temperature changing?
11. How is the SOC changing? Discharge Charge .
Return to the shop.

SELF ASSESSMENT 2-2
Data List Information – Test Drive
Name: Date:
Review this sheet as you are doing the Data List Information worksheet. Check off either category after
Topic Comment
Create User Data from the HV ECU Data List.
Determine if MG1 is being used as a motor or
generator.
Determine if MG2 is being used as a motor or
generator.
View the Battery ECU Data List.
Determine the SOC (State of Charge).

The sealed nickel−metal hydride (Ni−MH) battery technology developed
for the hybrid system provides both high power density and excellent
longevity. The hybrid system controls charge and discharge rates to
keep the HV battery at a constant State of Charge (SOC).
HV Battery Layout
The HV Battery, Battery ECU
and SMR (System Main Relay)
are enclosed in a single
case located in the luggage
compartment behind
the rear seat.
Section 3
High-Voltage Battery
Overview

Section 3
The power cable is a high−voltage, high−amperage cable that connects
the HV battery with the inverter and the inverter with MG1 and MG2.
In the ’04 & later Prius, the power cable also connects the inverter with
the A/C compressor.
The power cable is routed under the rear seat, through the floor panel,
along the under−the−floor reinforcement, and connects to the inverter in
the engine compartment. The 12V DC wiring harness follows a similar
route from the auxiliary battery to the front of the vehicle
The power cable is shielded to reduce electromagnetic interference.
For identification purposes, the high−voltage wiring harness and
connectors are color−coded orange to distinguish them from ordinary
low−voltage wiring.
Power Routing Cable
Power Cable

The HV battery pack contains six nickel−metal hydride 1.2V cells that
are connected in series to form one module.
In the ’01−03 Prius, 38 modules are divided into two holders and
connected in series. Thus, the HV battery contains a total of 228 cells
and has a rated voltage of 273.6V.
In the ’04 and later Prius, 28 modules are connected for a rated voltage
of 201.6V. The cells are connected in two places to reduce the internal
resistance of the battery.
The electrode plates in the HV battery are made of porous nickel and
metal hydride alloy.
For battery recycling information, please refer to the Warranty Policy
and Procedure manual.
HV Battery Pack ’04 Prius and Later ’01-‘03 Prius
Battery pack voltage 201.6V 273.6V
Number of Ni-MH battery
modules in the pack
28 38
Number of cells 168 228
Ni-MH battery module
voltage
7.2V
➝
HV Battery
Main Components
HV - Nickel-Metal
Hydride Battery
NOTE
HV Battery Pack
Information

Section 3
The battery ECU provides the following functions:
• It estimates the charging/discharging amperage and outputs charge
and discharge requests to the HV ECU so that the SOC can be
constantly maintained at a center level.
• It estimates the amount of heat generated during charging and
discharging, and adjusts the cooling fan to maintain HV battery
temperature.
• It monitors the temperature and voltage of the battery and if a
malfunction is detected, can restrict or stop charging and
discharging to protect the HV battery.
Battery ECU
Battery ECU

The battery ECU constantly monitors HV battery temperature, voltage
and amperage. It also checks for leaks in the HV battery.
While the vehicle is in motion, the HV battery undergoes repetitive
charge/discharge cycles as it becomes discharged by MG2 during
acceleration, and charged by the regenerative brake during
deceleration. The Battery ECU estimates the charge/discharge
amperage and outputs charge/discharge requests to the HV ECU to
maintain the SOC at a median level.
The target SOC is 60%. When the SOC drops below the target range,
the battery ECU informs the HV ECU. The HV ECU then signals the
engine ECM to increase power to charge the HV battery. If the SOC is
below 20%, the engine is not producing power.
The normal, low to high SOC deviation is 20%. If the Delta SOC
exceeds 20%, this means that the HV battery ECU cannot correct or
maintain the SOC difference within the acceptable range.
SOC
The battery ECU outputs
requests to the HV ECU so
the SOC can be maintained
at a center level.
State Of Charge
(SOC)
Delta SOC

Section 3
The System Main Relay (SMR) connects and disconnects power to the
high−voltage circuit based on commands from the HV ECU. A total of
three relays (one for the negative side and two for the positive side) are
provided to ensure proper operation.
When the circuit is energized, SMR1 and SMR3 are turned ON. The
resistor in line with SMR1 protects the circuit from excessive initial
current (called ‘inrush’ current). Next, SMR2 is turned ON and SMR1
is turned OFF, allowing current to flow freely in the circuit.
When de−energized, SMR2 and SMR3 are turned OFF in that order
and the HV ECU verifies that the respective relays have been properly
turned OFF.
System Main Relay
(SMR)
The SMR connects and
disconnects the power source
of the high-voltage circuit. A
total of three relays (one for
the negative side and two for
the positive side) are provided
to ensure proper operation.
System Main Relay
(SMR)

When the service plug is removed the high−voltage circuit is shut OFF
at the intermediate position of the HV battery.
The service plug assembly contains a safety interlock reed switch.
Lifting the clip on the service plug opens the reed switch, shutting OFF
the SMR.
The main fuse for the high−voltage circuit is inside the service plug
assembly.
For safety reasons, you must always turn the vehicle OFF before
removing the service plug.
The battery ECU detects battery temperature via three temperature
sensors in the HV battery and one intake air temperature sensor.
Based on those readings, the battery ECU adjusts the duty cycle of the
cooling fan to maintain the temperature of the HV battery within the
specified range.
The battery ECU keeps the fan OFF or running at LO if:
• The A/C is being used to cool the vehicle.
• Some margin is left in the temperature of the battery.
HV Battery Cooling
System
(’01-’03 Prius)
Service Plug
NOTE
HV Battery Cooling
System

Section 3
HV Battery
Cooling System
The Prius uses an Absorbed Glass Mat (AGM) 12V maintenance free
auxiliary battery. This 12V battery powers the vehicle’s electrical
system similar to a conventional vehicle. The battery is grounded to
the metal chassis of the vehicle and vented to ambient (outside) air
with a tube.
This battery is very sensitive to high−voltage. When charging the
auxiliary battery you should use the Toyota approved charger, because
a standard battery charger does not have the proper voltage control
and may damage the battery. If the approved charger is not available
you may use a trickle charger if the amperage is kept below 3.5 A.
The battery should be removed from the vehicle during charging.
However, it is safe to jump−start the Prius from either the battery or
the jump−start terminal under the hood. This will allow the vehicle’s
charging system to restore the battery to normal SOC.
If the vehicle will not be used for more than two weeks, disconnect the
12V battery to prevent it from discharging. Always make sure that all
doors are properly closed and that the interior lights are OFF, especially
overnight. These situations will quickly deplete the 12V battery.
Auxiliary Battery

Auxiliary Battery
In glass mat batteries, the
electrolyte is trapped in
separators to reduce the
amount of hydrogen gas
released when the battery
is charged.
Glass mat batteries are
sealed and the electrolyte
cannot be replaced.
Auxiliary Battery
Charging
There is a remote access B +
terminal in the main junction
block under the hood, so it is
no longer necessary to
remove interior trim pieces to
gain access to the battery.

Section 3

WORKSHEET 3-1
Hybrid Diagnostic Trouble Codes
In this worksheet you will diagnose hybrid malfunctions by viewing DTCs, Information Codes, and the HV ECU
Data List.
Tools and Equipment
• Vehicle
• Printer
• Repair Manual or TIS
Section 1: Hybrid Diagnosis
1. When starting the vehicle (READY light ON) do any warning lights illuminate? If so, which ones?
2. Connect the Diagnostic Tester to DLC3. Select Codes All to check all the ECUs.
3. How many systems are checked when using Codes All?
4. List the systems that show NG (No Good).
5. Now view the Information Codes by pressing enter on the systems that say NG, then press enter again.
Highlight the number next to INFORMATION and press enter.

Section 3
6. Use the Repair Manual or TIS to look up the DTC and Information Code in order to find what part of the
system is affected. List this information below.
7. Is there any information in the HV ECU Data List that can help you diagnose the vehicle? If so, print and
highlight the information.
8. After diagnosing the vehicle, clear the codes and return to the classroom.
Hint: To clear DTCs, you must exit out of CODES ALL and enter each section individually.

SELF-ASSESSMENT 3-1
Hybrid Diagnostic Codes
Name: Date:
Review this sheet as you are doing the Hybrid DTC Diagnosis worksheet. Check off either category after
Topic Comment
Locate vehicle warning lights.
View Codes All using the Diagnostic Tester.
View the Information Codes.
Use TIS & Repair Manual to research these
codes.
View the HV ECU Data List.
Clear Codes.

Section 3

The 1NZ−FXE is one of two power sources for the Prius. The 1NZ−FXE
is a 1.5 liter inline 4−cylinder engine with VVT−i (Variable Valve Timing
with intelligence) and ETCS−i (Electric Throttle Control System with
intelligence). The 1NZ−FXE includes a number of modifications that
help balance performance, fuel economy and clean emissions in hybrid
vehicles.
One unique aspect of the 1NZ−FXE is its Atkinson cycle valve timing,
which allows the engine to decrease emissions by varying the
relationship between the compression stroke and the expansion stroke.
Another feature incorporated on ’04 & later models is a special coolant
heat storage system that recovers hot coolant from the engine and
stores it in an insulated tank where it stays hot for up to three days.
Later, an electric pump pre−circulates the hot coolant through the
engine to reduce HC emissions normally associated with a cold start.
Engine
The 1NZ-FXE is a 1.5 liter
inline 4-cylinder engine.
Section 4
Engine
Overview

Section 4
Engine Specifications Model ’04 Prius ’03 Prius
Engine Specifications
Engine Type 1NZ−FXE ←
No. of Cyls. & Arrangement 4−Cylinder, In−line ←
Valve Mechanism
16−Valve DOHC,
Chain Drive (with VVT−i)
←
Combustion Chamber Pentroof Type ←
Manifolds Cross−Flow ←
Fuel System SFI ←
Displacement cm3 (cu. in.) 1497 (91.3) ←
Bore x Stroke mm (in.) 75.0 x 84.7 (2.95 x 3.33) ←
Compression Ratio 13.0 : 1 ←
Max Output (SAE−NET)
57 kw @ 5000 rpm
(76 HP @ 5000 rpm)
52 kw @ 4500 rpm
(70 HP @ 4500 rpm)
Max Torque (SAE−NET)
111 N⋅m @ 4200 rpm
(82 ft⋅1bf @ 4200 rpm)
←
Intake
Open 18° ~ −15° BTDC 18° ~ −25° BTDC
Valve
Intake
Close 72° ~ 105° ABDC 72° ~ 115° ABDC
Valve
Timing
Exhaust
Open 34° BBDC ←
Exhaust
Close 2° ATDC ←
Firing Order 1−3−4−2 ←
Research Octane Number 91 or higher ←
Octane Rating 87 or higher ←
Engine Service Mass * (Reference)
kg
(lb)
86.1 (189.8) 86.6 (190.9)
Oil Grade
API SJ, SL, EC or
ILSAC
API SH, SJ, EC or
ILSAC
Tailpipe Emission Regulation SULEV ←
Evaporative Emission Regulation AT−PZEV, ORVR LEV−II, ORVR
*: Weight shows the figure with the oil and engine coolant fully filled.
Figure 4.2 T071f402

Engine
VVT−i allows the engine control system to independently adjust intake
valve timing. The 1NZ−FXE uses this ability to move between
conventional valve timing and Atkinson cycle valve timing, varying the
effective displacement of the engine.
In an Atkinson cycle engine, the intake valve is held open well into the
compression stroke. While the valve is open, some of the cylinder
volume is forced back into the intake manifold. This creates an
effective reduction in engine displacement. By using the VVT−i system
to continuously adjust intake valve timing between Atkinson cycle
valve timing and conventional valve timing, the engine can maximize
fuel efficiency whenever possible while still producing maximum power
when required.
Valve Timing
The maximum retard closing
timing of the intake valve
by the VVT-i system has
been decreased from 115
degrees ABDC (After
Bottom-Dead-Center)
in the ’01-’03 Prius to
105 degrees ABDC in
the ’04 & later Prius.
VVT-i and
Atkinson Cycle

Section 4
Intake Manifold
The intake manifold has a
large surge tank that
accommodates the air forced
back into the manifold during
the compression stroke
of the Atkinson cycle engine.
Because some of the air is forced back into the intake manifold during
the compression stroke of the Atkinson cycle, the 1NZ−FXE’s intake
manifold includes a large surge tank to accommodate the extra volume.
Also, the length of the intake manifold’s intake pipe has been
shortened to improve air efficiency and the intake pipes have been
integrated midstream to reduce weight. Finally, the throttle body has
been positioned down flow in the center of the surge tank to achieve
uniform intake air distribution.
With ETCS−i on the Prius, there is no accelerator cable connected to
the throttle valve. Instead, the ECM looks at the output of the
Accelerator Pedal Position Sensor to determine driver demand, and
then calculates the optimal throttle valve opening for the current
driving condition. It then uses the throttle control motor to control the
throttle valve angle.
Intake Manifold
ETCS-i

Engine
The Mass Airflow Meter determines the amount of air flowing into the
intake manifold. To measure airflow, a heated platinum wire is
positioned in the intake air stream just above the throttle body. The
temperature of the hot wire is maintained at a constant value by
controlling the current flow through the hot wire. Incoming air tends to
cool the hot wire. As airflow increases, current flow through the wire
must be increased to maintain the hot wire’s set temperature. This
current flow is then measured and reported to the ECM as the output
voltage of the airflow meter.
The Intake Air Temperature Sensor is built into the Mass Airflow
Meter and uses an NTC (Negative Temperature Coefficient) thermistor
to monitor intake air temperature. As intake air temperature
increases, the thermistor’s resistance and the signal voltage to the
ECM decrease.
The Engine Coolant Temperature Sensor is located in the engine block
and uses an NTC thermistor monitor engine coolant temperature. As
coolant temperature increases, the thermistor’s resistance and the
signal voltage to the ECM decrease.
The Accelerator Pedal Position Sensor is mounted on the accelerator
pedal assembly. Two Hall ICs are used to detect accelerator pedal
position. Due to the characteristics of the Hall ICs, different signals are
output depending on whether the pedal is being pressed or released.
The HV ECU receives the signals and compares them to ensure that
there is no malfunction.
The Throttle Position Sensor is mounted on the throttle body and
converts throttle valve angle into two voltage signals (VTA and VTA2).
The ECM compares the two voltages to ensure there is not malfunction.
The ECM uses this information to calculate throttle valve opening,
then actuates the throttle control motor to adjust throttle valve
position accordingly.
ETCS−i adjusts the throttle valve angle to control idle speed. No
separate idle speed control system is required. The system includes
idle−up control during cold engine operation, intake air volume control
to improve engine startability, and load compensation for changes such
as when the A/C is turned ON or OFF.
Engine Control
System Sensors
Mass Airflow Meter
Intake Air
Temperature Sensor
Engine Coolant
Temperature Sensor
Accelerator Pedal
Position Sensor
Throttle Position
Sensor
Idle Speed Control

Section 4
The Knock Sensor is mounted on the cylinder block and detects
detonation or knocking in the engine. The sensor contains a
piezoelectric element that generates a voltage when cylinder block
vibrations due to knocking deform the sensor. If engine knocking
occurs, ignition timing is retarded until the knock is suppressed.
The Crankshaft Position Sensor (NE signal) consists of a toothed signal
plate mounted on the crankshaft and an inductive pick up coil. The
signal plate has 34 teeth, with one gap created by missing teeth, so the
sensor generates a 34−pulse waveform for every crankshaft revolution.
Since this is an inductive sensor, both the frequency and amplitude of
the generated signal increase with increasing engine rpm. The ECM
uses the NE signal to determine engine rpm and detect misfires.
The Camshaft Position Sensor (G2 signal) consists of a signal plate
with a single tooth that is mounted on the exhaust camshaft and a pick
up coil. The sensor generates one−pulse waveform for every revolution
of the exhaust camshaft. Since this is an inductive sensor, both the
frequency and amplitude of the generated signal increase as engine
rpm increases. The ECM uses the G2 signal to determine the position
of the number one piston for the ignition firing order.
On the ’01−’03 Prius, the sensors include:
• Bank 1, Sensor 1*
• Bank 1, Sensor 2*
*Sensor 1 − refers to the sensor ahead of the catalytic converter. This
sensor measures the oxygen content of the engine exhaust gases. The
ECM uses this input to adjust fuel trim.
*Sensor 2 − refers to the sensor after the catalytic converter. This
sensor is used to measure catalyst efficiency.
The O2 Heater Control maintains the temperature of the O2 Sensors to
increase accuracy of detection of the oxygen concentration in the
exhaust gas.
On the ’04 and later Prius, the Bank 1 Sensor 1 O2 sensor is replaced
by an A/F sensor. The A/F sensor detects the air/fuel ratio over a wider
range, allowing the ECM to further reduce emissions.
The Prius uses a planar (flat) A/F sensor. The sensor and heater on a
planar sensor are narrower than those on a conventional cup sensor.
This allows the heater to heat the alumina and zirconia more quickly,
accelerating sensor activation.
Knock Sensor
Crankshaft Position
Sensor
Camshaft Position
Sensor
Heated O2 Sensors
Air/Fuel Ratio
Sensor

Engine
Exhaust System
The HCAC system adsorbs and retains unburned hydrocarbons (HC)
produced by the engine during and following a cold start. Once the
engine has warmed up, the hydrocarbons are released and purged
through the warm three−way catalyst. This improves exhaust
emissions at low temperatures.
HC Adsorber and
Catalyst System
(HCAC)
(‘01-‘03 Prius)

Section 4
HCAC - Cold Engine
When the engine is started,
the ECM signals the HCAC
VSV to apply vacuum to the
HCAC actuator, closing the
bypass valve. Exhaust gases
pass through the HC adsorber
where HC is stored until the
temperature of the HC
adsorber rises. This prevents
HC from being emitted when
catalyst temperatures are low.
HCAC - Purge
When the TWC reaches
operating temperature
the VSV closes and the
bypass valve opens.
Stored HC is now purged
and flows through the TWC
where it is oxidized.
HCAC - Scavenge
During Deceleration
During deceleration, the VSV is
turned on, closing the bypass
valve. This scavenges
any HC that remains
in the HC adsorber.

Engine
The 1NZ−FXE uses a pressurized, forced−circulation cooling system. A
thermostat with a bypass valve located on the water inlet housing
controls coolant flow to maintain suitable temperature distribution in
the cooling system.
The radiator for the engine and the A/C condenser are integrated to
minimize space requirements. On the ’04 & later Prius, the radiator for
the inverter cooling system has also been integrated into the same
unit.
Cooling System
The coolant heat storage tank
on the ’04 & later Prius
can store hot coolant
up to three days.
This allows for quick
engine warm up and
reduces emissions.
Radiator & Condenser
On the ’04 & later Prius the
engine and inverter radiators
are integrated with the
A/C condenser.
Cooling System

Section 4
Starting with the ’04 Prius, the cooling system includes a Coolant Heat
Storage Tank that can store hot coolant at 176 degrees Fahrenheit for
up to three days. When starting a cold engine, the system uses an
auxiliary water pump to force the hot coolant into the engine. This
‘preheating’ of the engine reduces HC exhaust emissions.
Coolant Heat
Storage Tank
The storage tank is a
large vacuum insulated
container located near the
left front bumper.
Coolant Heat
Storage

Engine
Coolant Heat
Storage Tank
Coolant Heat
Storage Tank
When servicing the coolant system on the ’04 & later Prius:
• Disconnect the coolant heat storage water pump connector to
prevent circulation of the coolant and prevent possible injury.
• Drain the engine coolant.
• When refilling, operate the coolant heat storage water pump to help
the inflow of coolant into the tank.
SERVICE TIP

Section 4
Rotary Water Valve
Switches between three
positions to control flow
of coolant in and out of
coolant heat storage system.
Coolant Heat Storage
Tank Operation
Preheat Operation.

Engine
Tank Operation
Engine Warm-up
Operation.
Tank Operation
Storage Operation
(during driving)

Section 4
Tank Operation
Storage Operation
(IG-OFF)
The bladder fuel tank reduces the amount of fuel lost to evaporation. To
prevent evaporation the fuel is stored inside a flexible resin storage tank
sealed within a metal outer tank. The resin tank expands and contracts
with the volume of the fuel, so the space into which fuel can evaporate is
minimized. This approach dramatically reduces evaporative emissions.
Fuel Bladder
The resin bladder in the
Prius fuel tank expands and
contracts with the changing
quantity of fuel.
Bladder Fuel Tank

Engine
The direct acting fuel gauge is located in the sealed inner tank. This
gauge consists of a pipe surrounded by a coil. A magnet attached to a
float in the pipe moves up and down with changes in fuel level causing
a change in the coil’s magnetic field. This results in a slight difference
in potential at either end of the coil that is read by the Meter ECU.
The fuel pump is integrated with the fuel tank and cannot be serviced
separately.
Fuel Gauge Sender
Direct-acting fuel gauge,
consisting of a magnetic float,
is located in the sub tank.
Fuel Gauge
NOTE

Section 4
There are two inclination sensors located in the meter ECU that detect
vehicle longitudinal and latitudinal inclination to correct the fuel level
calculation. Corrections are made based on the signals from the
inclination sensors and the ambient temperature sensor located in the
fuel tank.
The inclinometer must be reset if the driver can only pump a few
gallons of gas into his/her tank, or the vehicle runs out of gas with
three or four bars left on the fuel meter. The inclinometer must also be
reset if the Prius is refilled on an excessive slope or if the fuel gauge
becomes inaccurate. Please refer to the Prius Repair Manual for the
inclinometer calibration procedure.
Fuel Gauge
Inclination Sensors
Unlike conventional vehicles, on a hybrid vehicle the engine may start
many times in a single drive cycle. This increases potential hot soak"
issues.
Inclination Sensors
NOTE

Engine
Fuel capacity can vary for several reasons:
• Temperature − At low ambient temperatures, the resin material
used for the flexible inner tank may lose some of its ability to
expand during refueling. If the outside temperature is 14F, the
size of the tank is reduced by approximately 5 liters.
• Fuel Nozzle Fit − The bladder fuel tank uses gas pump pressure to
help inflate the bladder during refueling, so the Prius fuel filler
neck is equipped with a rubber seal to ensure a tight seal between
the pump nozzle and the filler neck. If the gas pump nozzle is
dented, scratched, or gouged the poor fit between the pump nozzle
and the filler neck can reduce fuel tank capacity.
Overfilling (trying to force additional fuel into the tank) pushes excess
fuel into the EVAP system. This may cause EVAP DTCs and may even
require the replacement of some EVAP system components.
The Energy Monitor, which includes a historical bar graph and total
trip fuel economy (MPG), is very accurate. Multiple, comparative
calculations are performed by several computers.
Fuel usage and fuel economy are calculated by monitoring fuel injector
duration and operating frequency. The ECU compares these values
with miles traveled to calculate miles per gallon.
The battery ECU closely monitors energy consumption in Watts. By
calculating the amount of energy spent, recovered, and stored, the
computer can calculate the required fuel burn. Fuel required to create
this amount of energy is compared against the engine ECU fuel
injection calculation to insure accuracy.
Driving pattern, speed, and load characteristics are stored in the HV
ECU as Historical Data. Historical Data is used to further refine the
MPG calculation. This data takes about three to six weeks to
accumulate if the battery is disconnected or the HV ECU is replaced.
Use only 87 Octane unleaded gasoline in the Prius. The Prius has a
smaller fuel tank opening to help prevent nozzle mix−ups. At a
minimum, the gasoline used should meet the specifications of ASTM
D4814 in the United States. Do not use premium gasoline. It may
causes starting problems with the Prius. There is no gas mileage
benefit when using premium gas!
Fuel Capacity
NOTE
Energy Monitor
Fuel Type
Octane Rating

Section 4
To check for leaks in the EVAP system the Prius introduces purge
vacuum into the entire system, then looks for changes in pressure. Any
loss of vacuum indicates a leak in the system.
To detect EVAP leaks from the vapor reducing fuel tank, the Prius uses
the density method. This method uses an O2 sensor to measure HC
density in the exhaust gases. Added HC from a leak will cause a
reduction in exhaust oxygen content.
EVAP Parts Location
EVAP
System Checks

Engine
The EVAP system includes the following main components:
• Canister Closed Valve VSV – This normally open valve is located
between the fresh air line and the fuel tank. This Vacuum
Switching Valve (VSV) stops airflow into the EVAP system to seal
the system and enable leak detection. It is also known as the CAN
CTRL VSV or the CCV VSV.
• Purge Flow Switching Valve VSV – Allows vacuum from the EVAP
VSV (or Purge VSV) to flow through the canister. When activated
by the ECM during internal fuel bladder leak detection, it switches
airflow from the canister to the outer tank bladder only. This VSV
is also called the Tank Bypass VSV on the Diagnostic Tester.
• EVAP (Alone) VSV – Is used to control engine vacuum to the EVAP
system in order to remove stored hydrocarbons from the charcoal
canister. It is also used for system leak detection and may be
referred to as the Purge VSV.
• Vapor Pressure Sensor (VPS) − The ECU provides a 5V signal and
ground to the Vapor Pressure Sensor. The VPS sends a voltage
signal back to the ECU, which varies between 0.1 – 4.9V in
response to tank pressure.
• Fuel Cutoff Valve − Causes the filler nozzle to shut off when the
fuel tank is full to prevent overfilling.
• Refuel Check Valve − Anti−siphon valve that prevents fuel from
entering EVAP system lines. Also called Tank Over Fill Check
Valve.
The following VSVs are referred to by several different names in some
Toyota repair information:
• CAN CTRL VSV − Canister Closed Valve or CCV VSV
• Tank Bypass VSV − Purge Flow Switching Valve
• EVAP VSV (Alone) − Purge VSV
• Refuel Check Valve − Tank Over Fill Check Valve
EVAP Components
NOTE

Section 4
EVAP Control
Components
On the ’04 later Prius, the
fresh air inlet has been
relocated from the air cleaner
to the vicinity of the fuel inlet.

Engine
When refueling, the engine is OFF and EVAP VSV is CLOSED (OFF).
The resin bladder expands as fuel enters, so there is virtually no vapor
space above the fuel. Hydrocarbon (HC) vapor flows from the secondary
tank and fuel pump through the EVAP line to the charcoal canister
where the HC is absorbed and stored.
Airflows from the charcoal canister to the airspace between the metal
outer tank and bladder and to the Canister Closed Valve. The Canister
Closed Valve (CCV) is OPEN, allowing air to exit from the Fresh Air
Valve. The Refuel Check Valve and Fuel Cutoff Valve work together to
prevent overfilling and liquid fuel from entering the charcoal canister.
ORVR Refueling
Operation - ORVR
Refueling

Section 4
During normal purge operation the engine is running and the ECM
duty cycles the EVAP VSV ON and OFF allowing vacuum from the
intake manifold to pull air through the EVAP system. The Purge Flow
Switching Valve is OFF, opening the connection between the charcoal
canister and the EVAP VSV. HC vapor flows from the charcoal canister
to the EVAP VSV and into the intake manifold.
The Canister Closed Valve (CCV) is OPEN, allowing fresh air to enter
from the air cleaner and flow through the airspace between the metal
outer tank and bladder and up to the charcoal canister. As this air
passes through the canister, it purges the HC.
Purging
Purging

WORKSHEET 4-1
Out of Gas Condition
This worksheet will give you additional experience diagnosing hybrid system diagnostic codes and identifying a
common “Out of Gas” condition.
Tools and Equipment
• Vehicle
• Repair Manual or TIS
NOTE: DO NOT operate the vehicle with a SOC (State of Charge) below 35%!!! Reinstall the Circuit
Opening Relay and cycle the key to recharge the battery. Do not leave the parking lot area!!
Section 1 – Battery Data List
1. Connect the Diagnostic Tester to DLC3.
2. Access the Battery ECU Data List.
3. Create a User Data list (use YES/NO keys to turn ON) with the following:
• BATTERY SOC
• BATT TEMP 1
• BATT TEMP 2
• BATT TEMP 3
• BATT TEMP 4
• BATT BLOCK V1
• BATT BLOCK V2
4. What is the SOC (State of Charge)?
5. Using the Repair Manual, locate the Circuit Opening Relay. Leave the engine running and remove the
Circuit Opening Relay to shut OFF the fuel pump. What happened to the engine?

Out of Gas Condition TOYOTA HYBRID SYSTEM
6. After the circuit-opening relay is removed, turn the ignition OFF and attempt to restart the vehicle. Describe
what happens.
7. Drive under normal acceleration and observe the SOC. What is the SOC doing as the temperature
increases?
8. What is the SOC%?
9. Approximately how long can you operate the vehicle only on the HV Battery?
10. Exit out of the Data List and enter back into OBD/MOBD. Select CODES ALL.
11. On the Diagnostic Tester, highlight each system with a “NG” and press enter to retrieve the codes. Record
the DTCs and the related system below:
CODES SYSTEM

12. After the codes are recorded, clear all the codes by entering each area individually.
13. Re-install the circuit opening relay and cycle the ignition key OFF and back to the READY position to
re-start engine.
14. Using TIS, look up the TSB regarding Maintenance for HV and Aux. Batteries at Port and Dealers. Once
you are have opened the TSB, search for Onboard Equalizing Charge of HV Battery. Follow the
instructions and begin the battery equalization process to re-charge the HV battery.
NOTE: This procedure is only for the ’01-’03 Prius.
Notify the instructor when you are finished.

SELF-ASSESSMENT 4-1
Out of Gas Condition
Name: Date:
Review this sheet as you are doing the Out of Gas Condition worksheet. Check off either category after
Topic Comment
Create User Data from the Battery ECU Data
List.
Locate and remove the circuit-opening relay.
Determine the SOC.
Record DTCs.

WORKSHEET 4-2
Inclination Sensor Reset
In this worksheet you will reset the Inclination Sensor. This procedure can be useful in solving a customer
concern about improper fuel reading.
Tools and Equipment
• Vehicle
• Repair Manual
Section 1: Inclination Sensor Reset
Note: Be sure vehicle is on a level surface before resetting the Inclination Sensor.
1. Reset the Inclination Sensor when replacing a Combination Meter or responding to a customer concern
about improper fuel reading or repeatedly running out of gas. Please refer to the BE section of the Repair
Manual for complete reset procedures.
2. Answer the questions on the following page while doing the procedures below.
3. On the ’04 and later Prius:
• With the trip meter set to Trip A, depress and hold the Trip button while pressing the power button twice.
(Do not put your foot on the brake.)
• Push the trip switch two times within five seconds.
• Push and hold the trip switch for five seconds or more then release.
• Check that the inclination sensor information is displayed in the dash.
• Push and hold the trip switch for five seconds or more to update the centered value.
• When value is displayed for five seconds, the third digit will indicate the status. The value of 1 indicates
a successful reset.
4. On the ’01-’03 Prius:
• Depress and hold the Trip button while turning the ignition key to the ON position.
• Release and press the Trip button three more times within five seconds:
Release-Press-Release-Press-Release-Press and Hold.

Inclination Sensor Reset TOYOTA HYBRID SYSTEM
• Continue holding the Trip button for at least five seconds, then release.
• Check that the inclination sensor information is displayed in the dash.
(*) Current result display mode
0: Input state
1: Input state complete
2: E2ROM error
3: Speed input during input state
or cancel during ODO input state
(*2)
0: Horizontal
1: 3° to 5°
2: Over 5°
3: Error
Front rear
direction
sensor info.
Area code
for A/D
value (*2)
Sensor
A/D value
Right - left
direction
sensor info.
(*1)
Note: This procedure may take several attempts. Each time you start again, remove the key from the
ignition and wait at least five seconds.
5. List the six-digit number displayed.
6. What do the first three digits mean? What do the last three digits mean?
7. After recording the six-digit number, lean on the front or rear bumper. Are the numbers changing?
8. Release the bumper and allow the vehicle to return to normal ride height.
9. When you pressed and held the Trip button for at least five seconds at the end of the procedure a single
number should have appeared. What number was displayed?
10. According to the repair manual, what does this number mean?

Result Display Mode
0: Under processing
1: Recording completed
2: EEPROM error
3: Speed input or cancel during setting
If the number one (1) appeared, you are finished and the sensor is now reset. This allows for proper fuel
and gas mileage reading.

SELF-ASSESSMENT 4-2
Inclination Sensor Reset
Name: Date:
Review this sheet as you are doing the Inclination Sensor Reset worksheet. Check off either category after
Topic Comment
Locate Inclination Sensor information from TIS
or Repair Manual.
Determine what the reading means in relation
to the vehicle.

Toyota hybrid vehicles use a number of specialized chassis systems
including:
• A shift−by−wire system with electronic transmission control.
• A regenerative braking system that recovers much of the energy
normally lost to heat and friction during braking.
• An Electric Power Steering (EPS) system that improves fuel
economy because it only consumes energy when it is in use.
The ’01−’03 Prius uses a shift−by−wire system. The shift position sensor
is connected to a column−mounted shift lever and outputs two voltage
signals: a main signal and a sub signal. Both contain information about
shift position. The HV ECU determines shift position when both
signals match.
The ’04 later Prius uses a different shift−by−wire system. It uses two
sensors to monitor shift lever movement: a Select Sensor that detects
the lateral movement and a Shift Sensor that detects the longitudinal
movement. The combination of these signals is used to determine shift
position. When shift selection is complete, the reactive force of a spring
returns the lever to its home position.
Shift Control
(’01-’03 Prius)
Section 5
Chassis
Overview
Shift Control
(’01-’03 Prius)
Shift Control
(’04 later Prius)

Section 5
Shift Lock
(’01-’03 Prius)
Shift Assembly
(’04 later Prius)
The ’04 later Prius uses an electronic Shift Control Actuator to
engage the parking pawl. When the Shift Control Actuator receives a
lock signal from the transmission ECU it rotates, which moves the
parking lock rod and forces the parking lock pawl to engage the
parking gear. The Shift Control Actuator detects its own position when
the battery is reconnected, so it does not require initialization.
Shift Control
Actuator
(’04 later Prius)

Chassis
Shift Control
Actuator
(’04 later Prius)
If there is a malfunction in the shift control actuator, the vehicle will
not go into park. The Master Warning Light will illuminate, the shift
position indicators on the dash will flash, and the Park button light
will flash.
In this case, the vehicle cannot be turned OFF unless the parking
brake is applied. Then the vehicle can be turned OFF but cannot be
turned back ON again.
The Shift Control Actuator includes a cycloid gear reduction
mechanism that increases the actuator’s torque, ensuring that the
parking lock will release when the vehicle is parked on a slope.
This mechanism consists of an eccentric plate mounted on the motor’s
output shaft, a 61−tooth fixed gear that is secured to the motor housing
and a 60−tooth driven gear. As the output shaft rotates, the eccentric
plate presses the driven gear against the fixed gear. The driven gear,
which has one tooth less than the fixed gear, rotates one tooth for every
complete rotation of the eccentric plate. The result is a gear reduction
ratio of 61:1, along with an equivalent increase in torque.
SERVICE TIP
Cycloid Reduction
Mechanism
(’04 later Prius)

Section 5
Cycloid Reduction
Mechanism
1. Eccentric shaft rotates
with motor shaft, pressing
driven gear against
fixed gear.
2. Driven gear rotates one
tooth for every full rotation
of the motor shaft.
3. Reduction Ratio: 61:1.
The Diagnostic Tester cannot turn off the shift control system. To
power down the system remove the 30−amp main fuse located on the
left side of the fuse box on the driver’s side of the engine compartment.
This may be necessary if the vehicle needs to be pushed out of the shop.
Fuse Location
Removing the 30A PCON
MTR fuse disables the shift
control system.
SERVICE TIP

Chassis
The hybrid vehicle brake system includes both hydraulic brakes and a
unique regenerative braking system that uses the vehicle’s momentum
to recharge the HV battery. As soon as the accelerator pedal is
released, the HV ECU initiates regenerative braking. MG2 is turned by
the wheels and used as a generator to recharge the HV battery. During
this phase of braking, the hydraulic brakes are not used. When more
rapid deceleration is required, the hydraulic brakes are activated to
provide additional stopping power.
To increase energy efficiency the system uses the regenerative brakes
whenever possible. Selecting B on the shift lever will maximize
regenerative efficiency and is useful for controlling speeds downhill.
In ‘B’ mode, about 30% of the energy is recovered.
If either the regenerative or hydraulic braking system fails, the
remaining system will still work. However, the brake pedal will be
harder to press and the stopping distance will be longer. In this
situation, the brake system warning light will illuminate.
The battery will accept charge up to an instantaneous rate of 20 to 21
KWH. Much of the energy from light braking at high speeds and
harder braking at lower speeds can be recovered. Excess energy over
the charging limits is wasted as heat in the brakes. At this time there
is no way for the driver to know the limit of regenerative energy
recovery.
Brake System
Components
(’01-‘03 Prius)
Brake System
NOTE

Section 5
Brake System Diagram
(’01-‘03 Prius)
The ’01−’03 Prius applies hydraulic pressure from the master cylinder
directly to the front brakes. For the rear brakes, it uses a hydraulic
brake booster to increase brake force. Within the hydraulic brake
booster, a pump draws brake fluid from the reservoir tank and forces it
into the accumulator under high pressure. The accumulator stores the
high−pressure fluid until it is needed.
To make sure system pressure stays at the right level, two pressure
switches monitor hydraulic pressure coming from the accumulator:
• Pressure Switch PH − controls pump activation.
• Pressure Switch PL – generates a warning when system pressure is
too low.
If one of the pressure switches malfunctions it can cause the pump to
operate continuously, creating excessive pressure in the system. If that
happens, a relief valve shunts brake fluid to the reservoir tank to
relieve the excess pressure.
If the brake booster fails, the Brake System Warning Light and Buzzer
will illuminate. Pressing the brake pedal repeatedly may turn ON the
Brake System Warning Light and Buzzer briefly. If the brake booster is
operating normally, the light and buzzer will turn OFF after a few
seconds after start up.
Hydraulic Brake
Booster
(’01-’03 Prius)

Chassis
In the ’04 later Prius, the conventional brake booster has been
replaced by a hydraulic power source that is controlled by the Skid
Control ECU.
The hydraulic power source uses many of the same components used
on the previous system, including a pump, pump motor, accumulator,
relief valve, 2 motor relays, and an accumulator pressure sensor. To
improve the system, the accumulator has been made more gas−tight,
and a plunger−type pump has been adopted.
The control portion of the brake actuator includes:
• 2 master cylinder solenoid valves
• 4 pressure appliance valves
• 4 pressure reduction valves
• 2 master cylinder pressure sensors
• 4 wheel cylinder pressure sensors
In the ’01−’03 Prius, the Brake ECU controls the following brake
functions:
• Conventional brake control
• ABS with EBD control
• Regenerative brake cooperative control
The Brake ECU exchanges sensor information with the HV ECU.
Brake Actuator
(’04 later Prius)
Brake ECU
(’01-’03 Prius)

Section 5
Brake Control
Components
(’01-‘03 Prius)
In the ’04 later Prius, brake control processing is moved to the Skid
Control ECU, which handles:
• Conventional brake control
• ABS with EBD control
• Brake Assist
• Enhanced VSC
• Regenerative brake cooperative control
The Skid Control ECU exchanges sensor information EPS ECU and
the HV ECU.
Skid Control ECU
(’04 later Prius)

Chassis
Brake Control
Components
(’04 later Prius)
The ’04 later Prius uses an Electronically Controlled Brake (ECB)
system. To determine the amount of brake force requested, the Brake
Pedal Stroke Sensor uses a variable resistor to detect the amount of
brake pedal movement, and then transmits that information to the
Skid Control ECU.
When installing a Brake Pedal Stroke Sensor:
• Initially, the sensor lever is locked into the 0 stroke position by a
small pin. Do not detach the pin until the installation has been
completed.
• Install the sensor.
• Then, firmly press the brake pedal once to break off the pin.
• Make sure the broken pin does not remain in the sensor lever.
Brake Pedal
Stroke Sensor
(’04 later Prius)
SERVICE TIP

Section 5
Brake Pedal
Stroke Sensor
During regenerative braking fluid flow to the front calipers is limited.
To retain a normal pedal stroke during regenerative braking, the
Stroke Simulator consumes some of the fluid flow from the master
cylinder so that the pedal can move normally.
The stroke simulator is located between the master cylinder and the
brake actuator. It uses two coil springs with different spring constants
to provide pedal stroke characteristics in two stages.
Stroke Simulator
Stroke Simulator

Chassis
In the ’04 later Prius a Power Source Backup Unit has been added so
that the ECB will function long enough to stop the vehicle even if the
12V battery is compromised. The unit contains 28 capacitor cells that
store an electrical charge provided by the vehicle’s 12V power supply.
The capacitor cells discharge when the power switch is turned OFF.
If the Power Source Backup Unit is removed, it must first be checked
for residual voltage.
Power Source
Backup Unit
Power Source
Backup Unit
(’04 later Prius)

Section 5
Regenerative brake cooperative control balances the brake force of the
regenerative and hydraulic brakes to minimize the amount of kinetic
energy lost to heat and friction. It recovers the energy by converting it
into electrical energy.
On the ’04 later Prius, the increased power output of MG2 provides
increased regenerative brake force. In addition, the distribution of the
brake force has been improved through the adoption of the ECB
system, effectively increasing the range of the regenerative brake.
These attributes enhance the system’s ability to recover electrical
energy which contributes to fuel economy.
Regenerative
Brake System
To convert kinetic energy to
electrical energy, the system
uses MG2 as a generator.
The drive axle and MG2 are
joined mechanically. When
the drive wheels rotate MG2,
it tends to resist the rotation
of the wheels, providing both
electrical energy and the
brake force needed to slow
the vehicle. The greater the
amperage (battery charging
amperage), the greater
the resistance.
Regenerative Brake
Cooperative Control

Chassis
In the ’04 later Prius, brake force distribution (which was performed
mechanically in the past) is now performed under electrical control of
the skid control ECU. The skid control ECU precisely controls the
braking force in accordance with the vehicle’s driving conditions.
Generally, when the brakes are applied the vehicle’s weight shifts
forward, reducing the load on the rear wheels. When the Skid Control
ECU senses this condition (based on speed sensor output) it signals the
brake actuator to regulate rear brake force so that the vehicle will
remain under control during the stop. The amount of brake force
applied to the rear wheels varies based the amount of deceleration.
The amount of brake force that is applied to the rear wheels also varies
based on whether or not the vehicle is carrying a load.
Front/Rear Brake
Force Disk
When the brakes are applied while the vehicle is cornering, the load
applied to the inner wheel decreases while the load applied to the outer
wheel increases. When the Skid Control ECU senses this condition
(based on speed sensor output) it signals the brake actuator to regulate
brake force between the left and right wheels to prevent a skid.
Electronic Brake
Distribution (EBD)
Control
(’04 later Prius)
Brake Force
Distribution -
Front/Rear
(’04 later Prius)
Brake Force
Distribution -
Left/Right
(’04 later Prius)

Section 5
In emergencies, drivers often panic and do not apply sufficient pressure
to the brake pedal. So on the ’04 later Prius, the Brake Assist system
interprets a quick push of the brake pedal as emergency braking and
supplements braking power accordingly.
To determine the need for an emergency stop, the Skid Control ECU
looks at the speed and the amount of brake pedal application based on
signals from the master cylinder pressure sensors and the brake pedal
stroke sensor. If the Skid Control ECU determines that the driver is
attempting an emergency stop it signals the brake actuator to increase
hydraulic pressure.
A key feature of the Brake Assist system is that the timing and the
degree of braking assistance are designed to ensure that the driver
does not discern anything unusual about the braking operation. As
soon as the driver eases up on the brake pedal, the system reduces the
amount of assistance it provides.
Brake Assist
Brake Assist System
(’04 later Prius)

Chassis
The Enhanced VSC system available on the ’04 later Prius helps
maintain stability when the vehicle’s tires exceed their lateral grip.
The system helps control the vehicle by adjusting the motive force and
the brakes at each wheel when:
• The front wheels lose traction but the rear wheels don’t.
(front wheel skid tendency known as ‘understeer’)
• The rear wheels lose traction but the front wheels don’t.
(rear wheel skid tendency, or ‘oversteer’)
When the Skid Control ECU determines that the vehicle is in
understeer or oversteer, it decreases engine output and applies the
brakes to the appropriate wheels individually to control the vehicle.
• When the skid control ECU senses understeer, it brakes the front
and rear inside wheel. This slows the vehicle, shifts the load to the
outside front wheel and limits front wheel skid.
• When the skid control ECU senses oversteer, it brakes the front
and rear outside wheel. This restrains the skid and moves the
vehicle back toward its intended path.
Enhanced VSC provides the appropriate amount of steering assist
based on driving conditions by coordinating EPS and VSC control.
Cooperative Control
with EPS
Enhanced VSC
System
(’04 later Prius)
Cooperative Control
with EPS
(’04 later Prius)

Section 5
A 12V motor powers the EPS system so that steering feel is not
affected when the engine shuts off. The EPS ECU uses torque sensor
output along with information from the Skid Control ECU about
vehicle speed and torque assist demand to determine the direction and
force of the power assist. It then actuates the DC motor accordingly.
EPS Parts Location
The EPS ECU uses signals from the torque sensor to interpret the
diver’s steering intentions. It combines this information with data from
other sensors regarding current vehicle conditions to determine the
amount of steering assist that will be required. It can then control the
current to the DC motor that provides steering assist current to the DC
motor that provides steering assist.
Electric Power
Steering
EPS ECU

Chassis
EPS Steering System
When the steering wheel is turned, torque is transmitted to the pinion
causing the input shaft to rotate. The torsion bar that links the input
shaft and the pinion twists until the torque and the reaction force
equalize. The torque sensor detects the twist of the torsion bar and
generates an electrical signal that is proportional to the amount of
torque applied to the torsion bar. The EPS ECU uses that signal to
calculate the amount of power assist the DC motor should provide.
The ’01−‘03 Prius torque sensor is a surface−contact resistor and the ’04
later Prius uses an induction−type torque sensor.
The DC motor uses a worm gear to transmit the motor’s torque to the
column shaft.
Torque Sensor
(‘01-‘03 Prius)
Power Steering
System
DC Motor

Section 5
Torque Sensor
(’04 later Prius)
Detection Ring 1 and 2 are
mounted on the input shaft
and Detection Ring 3 is
mounted on the output shaft.
When torque is applied to the
torsion bar the detection rings
move in relationship to each
other. The detection coil
senses a change in
inductance that is
proportional to the amount
of torque applied.
For ’01 to ’03, the reduction mechanism transmits power assist from
the motor to the pinion shaft. The reduction mechanism consists of a
pinion gear integrated with the motor shaft and a ring gear that is
secured to the pinion shaft.
For ’04 later, the reduction mechanism transmits power assist from
the motor to the column shaft. The reduction mechanism consists of a
worm gear integrated with the motor shaft and wheel gear that is
connected to the column shaft.
Reduction
Mechanism
(’01-‘03 Prius)
Reduction
Mechanism
(’04 later Prius)

Chassis
If the EPS ECU detects a malfunction in the EPS system, a warning
light illuminates to alert the driver. The EPS ECU will store the
DTC(s) and the system will power down, however the system still
provides the ability to steer manually.
DC Motor
Fail Safe

Section 5

Toyota Hybrid System Overview.pdf

Toyota Hybrid System Overview.pdf

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