engine TOYOTA PRIUS 2001 Service Repair Manual

THS (TOYOTA HYBRID SYSTEM)
182TH24
ªREADYº LightOutput Control
Warning Light 26
DRIVING CHARACTERISTICS
Because the Prius uses a parallel series hybrid system, some aspects of its operation may differ from those of
existing automobiles, and may require precautions that are unique to this system.
1. Starting the THS
Make sure that the parking brake is engaged and that the shift lever is in the P position.
While depressing the brake pedal, turn the ignition switch to the START position. After this, the ªREADYº
light flashes.
The engine does not start when the shift lever is in the N position; it can only start in the P position. When
the external air temperature is low, the ªREADYº light may flash longer than usual.
As soon as the engine has started, the ªREADYº light illuminates steadily and a beeping sound is heard.
Several seconds after the engine warms up, the engine stops automatically, provided that the air conditioning
compressor does not need to operate and that the HV battery maintains a proper SOC (state of charge).
2. Start-Off
While keeping the brake pedal depressed, release
the parking brake, and move the shift lever to the
D position.
The vehicle has the same creeping movement as
the conventional automatic transmission vehicles.
Gradually release the brake pedal and slowly de-
press the accelerator pedal to start off.
At this time, the vehicle starts off powered only by
the MG2 (Motor Generator No.2)
NOTICE: The vehicle can be started off, provided that the ªREADYº light remains illuminated, even
if the engine remains stopped.
3. Acceleration
Depress the accelerator pedal to accelerate the vehicle.
If the engine remained stopped during start-off, the engine will start automatically during acceleration.
4. Downhill Driving
Move the shift lever to the B position as necessary in order to simultaneously apply the regenerative brake
and the engine friction brake.
5. Deceleration and Stopping
Depress the brake pedal to decelerate and to stop the vehicle.
Depressing the brake pedal causes the regenerative brake to activate automatically in the D or B position. (In
the regenerative brake system, kinetic energy is converted to electrical energy.) If the engine has warmed up,
the air conditioning compressor does not need to operate, and if the HV battery maintains a proper SOC (state
of charge), the engine stops automatically when the vehicle speed drops-even if the vehicle comes to a stop.
6. Parking
Push down the parking brake pedal, move the shift lever to the P position, and pull out the ignition key.
NOTICE: Make sure to pull out the ignition key after parking the vehicle because the vehicle can be
driven as long as the ªREADYº light remains illuminated even if the engine is stopped.
7. Other Characteristics and Precautions

If a drive wheel slips on slippery terrain, causing the front wheels to spin faster than the rear wheels, the
THS effects control to limit the slippage by restraining the drive force. (This also protects the planetary
gear from damage.)

When the HV battery temperature is too high or low, the output control warning light illuminates, alerting
the driver that output power may be limited.
This is not 2 malfunction. This condition may be corrected by avoiding sudden acceleration /decelaration,
after which the light will go out.

When the vehicle is stopped and the shift lever is in the N position, electricity is not generated even if the
engine is running. If the vehicle remains stopped for a long time, make sure to move the shift lever to the
P position. In heavy traffic, keep the shift lever in the D position.

THS (TOYOTA HYBRID SYSTEM)27
THS CONTROL SYSTEM
1. General
The THS control system contains the following components:
HV (Hybrid Vehicle
Control) ECU
Controls the MG1, 2 and the engine according to the demand torque,
regenerative brake control and the SOC (state of charge) of HV battery. These
factors are determined by the shift position, the degree which the accelerator
is depressed, and vehicle speed.
ECM
ControlThe HV ECU receives engine status data (rpm, torque) from the ECM and
determines the engine demand torque.
Moreover, engine stop and fuel cut signals are sent according to the driving
conditions.
In addition, the vehicle speed signal received from the combination meter is
also sent.
BRAKE
ECU
ControlThe HV ECU receives data corresponding to the total braking force needed.
The HV ECU transmits the regeneration brake demand torque valve, as well
as the regeneration brake execution torque valve.
Inverter
(for MG1,
MG2)
ControlThe HV ECU sends the signal to the power transistor in the inverter for
switching the U, V, W, phase of the MG1, 2 in order to drive the MG1 and 2.
Moreover, if an overheating, overcurrent or fault voltage signal is received
from the inverter, it is shut down.
ConverterWhen a malfunction is in the Hybrid vehicle control system, the HV ECU
sends a signal to the converter, and the converter is stopped.
MG1, MG2Detects the position of the rotor of the MG1, 2 and controls the current flowing
to the MG1, 2.
In addition, the temperature is detected and the maximum load is controlled.
Battery ECUReceives the SOC of the HV battery and the current value.
Airbag Sensor
AssemblyReceives the airbag deployment signal.
A / C ECUReceives the engine power rise demand (when air-conditioning is turned ON)
and the engine running demand for water-temperature maintenance.
Accelerator Pedal
Position SensorReceives the value corresponding to degree at which the accelerator pedal is
depressed.
Shift Position SensorReceives the shift position signal (P, R, N, D, B).
Cruise Control SwitchReceives the cruise control switch signal.
Stop Light SwitchReceives the brake signal.
Interlock Switch
(for Inverter Cover and
Service Plug)Verifies that the cover of both the inverter and the service plug have been
installed.
Circuit Breaker SensorThe high-voltage circuit is intercepted if a vehicle collision has been detected.
DiagnosisWhen the HV ECU detects a malfunction, the HV ECU diagnosis and
memorizes the values corresponding to the failure.
Fail-SafeWhen the HV ECU detects a malfunction, the HV ECU stops or controls the
actuators and ECUs according to the data already stored in memory.

THS (TOYOTA HYBRID SYSTEM)
HV ECUGO
ECM
Engine
Throttle Control
Motor
SPDO
EF1
HTE, ETH
ESA
VVT-i
W
MESTP
Brake Actuator
(Brake Master
Cylinder)
BRAKE ECUBrake Actuator
(Solenoid Valves)
Pressure Sensors
Signal
HV ECU Pressure
BTH
Total Brake Force
RequestedHTB
Regenerative Brake
Force Transmitted29
3. ECM Control
The ECM receives the demand torque and the target rpm which were sent from HV ECU (THE, ETH), and
controls the degree of throttle valve opening, fuel injection timing, ignition time and VVT-i.
In addition, the actual rpm is sent to the HV ECU with GO, and the speed signal from the hybrid transaxle
is received through HV ECU with SPDO.
When the vehicle is stopped, the HV ECU may send an engine stop (ESTP) command to the ECM to reduce
fuel used.
When a malfunction occurs in the system, the ECM activates MIL via the directions from the HV ECU.
4. BRAKE ECU Control
The brake ECU calculates the total braking force needed, based on the master cylinder pressure in the brake
actuator generated when the driver depresses the brake pedal, and sends this valve to the HV ECU.
The HV ECU computes a part for the regeneration brake force from the total braking force, and sends the
result to the brake ECU.
The HV ECU executes to the minus torque to MG2, and carries out the regenerative brake functions.
The brake ECU controls the brake actuator solenoid valves and generates the wheel cylinder pressure, which
is the regenerative brake force subtracted from the total braking force.

THS (TOYOTA HYBRID SYSTEM)
HV ECUG-SDOWNInverter
(for MG1)
MG1
MG2
M-UU, VU, WUSwitching Signal
Switching Signal
G-SIN, COS
M-SIN, COS
Inverter
(for MG2) G-UU, VU, WU
M-SDOWN
G-REF
M-REF
30
5. Inverter Control (for MG1, MG2)
The HV ECU transmits a signal to the power transistor in the inverter (G-UU, VU, WU, M-UU, VU, WU)
for switching the U, V, W phase of the stator coil of MG1 and MG2, based on the rotor position information
sent from MG1, 2 (G-SIN, COS, M-SIN, COS) and the SOC of the HV battery sent from the battery ECU.
When shutting down the current to MG1, 2, a signal is sent to the inverter from the HV ECU (G-SDOWN,
M-SDOWN).
Clutchless System
A clutchless system has been adopted to keep the front wheels and MG2 linked mechanically via gears and
a chain. To disengage the drive force in the neutral position, the N position signal from the shift position
sensor turns OFF all the power transistors in the inverter (which connects the MG1 and the MG2) in order
to shut down the operation of the MG1 and the MG2, thus rendering the drive force at the wheels to zero.
In this state, even if the engine is running, the MG1 merely freewheels in the no-load state.
Therefore, if the vehicle is allowed to operate continuously in the N position in a stationary state such as
in heavy traffic, the SOC (state of charge) of the HV battery will continue to drop lower and lower.
6. Battery ECU
The SOC, temperature and the voltage of HV battery are detected by the battery ECU, and this information
is sent to HV ECU.

THS (TOYOTA HYBRID SYSTEM)
182TH22
1. READY Light
2. Output Control
Warning Light 3. Master Warning Light
4. Malfunction Indicator light 5. Discharge Warning Light
6. EMPS Malfunction
Warning Light7. HV Battery Warning Light
8. Hybrid System
Malfunction Warning
Light 32
INDICATOR AND WARNING LIGHT
The warning lights of the Prius are different from those on conventional vehicles. Inspection and repair
should be performed while referring to the troubleshooting section in the 2001 Prius repair manual
(RM778U).

Center Meter 
Multi Information Display 
1. READY lightTurns on when the ignition switch is turned to START to indicate that the ve-
hicle is ready to drive.
2. Output control
warning lightTurns on when the remaining HV battery charge becomes insufficient at R
range or when there is an abnormal temperature rise in the HV battery due
to continuous driving under heavy loads. It may also light when the HV bat-
tery temperature is low (after starting at low temperatures). The hybrid sys-
tem output is limited while this light is on.
Travel at reduced speeds (avoid sudden acceleration) while the light is lit.
3. Master warning
lightTurns on with buzzer sounding by linked operation with warning lights ª6º
to ª8º on the multi center display.
4. Malfunction
indicator lightTurns on when there is a malfunction in the engine control system.
5. Discharge warning
lightTurns on when there is a malfunction in the 12 V charging system (converter
assembly).
If it turns on together with the master warning light and hybrid system
warning light, check the diagnostic code.
6. EMPS malfunction
warning lightTurns on when there is a malfunction in the EMPS control system.
7. HV battery warning
lightTurns on when the HV battery is discharged to the lower limit.
8. Hybrid system
warning lightTurns on when a malfunction in MG1, 2, inverter, HV battery or HV ECU
is detected.

THS (TOYOTA HYBRID SYSTEM)
182CH05
Stator
Rotor
Speed Sensor (Resolver)
MG1
182CH04
Stator
Rotor
Speed Sensor (Resolver)
MG2
182TH07
N.m
350
300
250
200
150
100
50
0
01000 30002000 50004000 60000 20 40
30
10 kW
Torque
Engine Speed (rpm)Output
Torque
Output
33
MG1 AND MG2 (MOTOR GENERATOR NO.1 AND NO.2)
DESCRIPTION
Both the MG1 and the MG2 are compact, lightweight, and highly efficient alternating current permanent
magnet synchronous type.
Serving as the source of supplemental motive force that provides power assistance to the engine as needed,
the electric motor helps the vehicle achieve excellent dynamic performance, including smooth start-offs
and acceleration. When the regenerative brake is activated, MG2 converts the vehicle's kinetic energy into
electrical energy, which is then stored in the HV battery.
MG1 recharges the HV battery and supplies electrical power to drive MG2. In addition, by regulating the
amount of electrical power generated (thus varying the generator's rpm), MG1 effectively controls the
continuously variable transmission function of the transaxle. MG1 also serves as the starter to start the
engine.

MG2 Specifications 
TypePermanent Magnet
Motor (1CM)
Rated voltage [V]273.6
Maximum output [kW] (rpm)33 / (1040
5600)
Maximum torque [N.m (kgf.m) (rpm)350 / (0
400)
Amperage at maximum torque [A]351
Cooling systemWater-cooled

Performance Curve 

THS (TOYOTA HYBRID SYSTEM)
182TH29
Rotational
Magnetic FieldU PhaseStator Coil
Rotor
Repulsion
W Phase V Phase
: From inverter
: Connected internally in the motor
Attruction
182TH09
Magnetized Side
Coil A
Coil B
Coil C Speed Sensor
(Resolver)Output Side
182TH10
Inverter Power Cable HV Battery
Junction
BlockPortion routed through
the center floorAuxiliary
Battery
Under-
the-Floor
Reinforcement
12 V
Power Cable
Voltage 
Power Cable
Voltage

34
1. Permanent Magnet Motor
When a three-phase alternating current is passed
through the three-phase windings of the stator
coil, a rotational magnetic field is created in the
electric motor. By controlling this rotating mag-
netic field according to the rotor's rotational posi-
tion and speed, the permanent magnets that are
provided in the rotor become attracted by the ro-
tating magnetic field, thus generating torque.
The generated torque is for all practical purposes
proportionate to the amount of current, and the
rotational speed is controlled by the frequency of
the alternating current.
Furthermore, a high level of torque, all the way to
high speeds, can be generated efficiently by prop-
erly controlling the rotating magnetic field and the
angles of the rotor magnets.
2. Speed Sensor (Resolver)
This is an extremely reliable and compact sensor
that precisely detects the magnetic pole position,
which is indispensable for ensuring the efficient
control of MG1 and MG2.
The sensor's stator contains 3 coils as illustrated, and
output coils B and C are electrically staggered 90 de-
grees. Because the rotor is oval, the distance of the
gap between the stator and the rotor varies with the
rotation of the rotor. Thus, 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.
In addition, the amount of positional variance
within a predetermined time is calculated by the
HV ECU, thus enabling this sensor to be used as
an rpm sensor.
3. Power Cable
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. Starting from
the connector at the left front of the HV battery lo-
cated in the luggage compartment, the power cable
is routed under the rear seat, through the floor panel,
along the under-the-floor reinforcement, and con-
nects to the inverter in the engine compartment. A
shielded cable is used for the power cable in order to
reduce electromagnetic interference.
The 12 V  wiring of the auxiliary battery also
follows the same route.
For identification purposes, the high-voltage wir-
ing harness and connectors are color-coded
orange to distinguish them from those of the ordi-
nary low-voltage wiring.

THS (TOYOTA HYBRID SYSTEM)
182TH26
Inverter
Converter
182TH15
Inverter
HV
Battery
Ignition Signal
Ground
Voltage
Detection
Circuit
Voltage
Detection
Circuit
Bridge Circuit for MG2
Amperage
Sensor
Signal Processor /
Protective Function Processor
Bridge Circuit for MG1
Amperage
Sensor
MG2
HV ECU
MG1
182TH27
Reservoir Tank
Radiator
Water Pump35
INVERTER
1. General
The inverter is an electric power converter that
converts the direct current of the Hybrid vehicle's
high-voltage battery (DC 273.6 V) and the alter-
nating current of the MG1 and MG2.
Consisting of 2 three-phase bridge circuits for
MG1 and MG2, respectively, and each containing
6 power transistors, the inverter converts direct
current and three-phase alternating current. The ac-
tivation of the power transistors is controlled by the
HV ECU. In addition, the inverter transmits in-
formation that is needed for current control, such as
the output amperage or voltage, to the HV ECU.
Together with MG1 and MG2, the inverter is
cooled by the dedicated radiator of the coolant
system that is separate from that of the engine.
2. System Diagram
3. Cooling System
A cooling system via water pump for the inverter
and MG1, 2 has been added.
The HV ECU controls the water pump with cool-
ant temperature.
It is separated with the engine cooling system.

THS (TOYOTA HYBRID SYSTEM)
182TH26
Inverter
Converter
182TH17
F. L
MAINF.L DCDC12 V

Output
Auxiliary
Battery S34B20
Shielded 12 VInverter
SDC273.6 V
DC / DC Converter
Input Filter
20 V
Converter Control Circuit
HV ECU A / C ECUIG
IDH NODD 36
CONVERTER
1. General
The power source for auxiliary equipment of the
vehicle such as the lights, audio system, and the air
conditioner cooling fan, as well as the ECUs, is
based on a 12 V system. Because the THS genera-
tor outputs at 273.6 V, the converter is used to
transform the voltage from DC273.6 V to DC 12
V in order to recharge the auxiliary battery. The
converter is installed on the underside of the in-
verter.
2. Operation

The DC273.6 V input is initially converted into alternating current by the transistor bridge circuit and
transformed into a low voltage by the transformer. After this, the current is rectified, smoothed (into direct
current) and converted into DC12 V.

The voltage at the positive terminal of the auxiliary battery is monitored by the converter and is maintained
at a constant level. Consequently, the voltage of the auxiliary battery is unrelated to the engine rpm (even
if the engine is stopped) and to the auxiliary equipment (output current of converter).

THS (TOYOTA HYBRID SYSTEM)
182TH21
Lead-calcium Alloy 42
AUXILIARY BATTERY
DESCRIPTION
The shielded, maintenance-free 12V battery (S34B20L) for the Prius is used.
Battery fluid is filtered into separators in order to reduce hydrogen gas released which occurs when the battery
is charged.
Therefore, battery fluid does not need to be replaced, as long as the specified battery is used.
HV IMMOBILISER SYSTEM
The HV immobiliser system has been designed to prevent the vehicle from being stolen. This system uses a
ECM that stores the ID code of the authorized ignition key. If an attempt is made to start the HV system using
an unauthorized key, the ECM prohibit fuel delivery and ignition, effectively disabling the engine.