TOYOTA PRIUS 2001 Service Repair Manual

THS (TOYOTA HYBRID SYSTEM)
182TH19
EngineECMHV ECU
Shift Position Sensor
Brake ECU
HV Battery
Accelerator Pedal Position Sensor
Hybrid Transaxle Inverter with Converter
Battery ECU
SMR (System Main Relay)
Service Plug23

FEATURES OF THS
This system controls the following modes in order to achieve the most efficient operations to match the driv-
ing conditions:
1. Supply of electrical power from the HV battery to MG2 provides force to drive the wheels
2. While the tires are driven by the engine via the planetary gears, MG1 is driven via the planetary gears to
supply electricity to MG2 to drive the wheels
3. When the vehicle is decelerating, kinetic energy from the wheels is recovered and converted into electrical
energy and used to recharge the HV battery by means of MG2.
The HV ECU switches between these modes (1, 2, 1 + 2, or 3) according to the driving conditions. However,
when the SOC of the HV battery is low, the HV battery is charged by the engine by turning MG1.
As a result, it achieves far greater the fuel economy compared to conventional gasoline engine vehicles, at
a reduced level of exhaust gas emissions. Furthermore, this revolutionary powertrain has eliminated the
constraints that are associated with electric vehicles (such as their short cruising range or their reliance on
external recharging units).

LAYOUT OF MAIN COMPONENTS

THS (TOYOTA HYBRID SYSTEM) 24

MAIN FUNCTIONS OF COMPONENTS
MG1Generates high-voltage electricity by being powered primarily by the engine.
Also functions as a starter to start the engine.
Hybrid
Trans-
axle
MG2
Primarily provide additional power to the engine in order to increase the
overall drive force. During braking, or when the accelerator pedal is not
depressed, it generates electricity to recharge the HV battery (Regenerative
brake system).
Planetary
Gear UnitDistributes the engine's drive force as appropriate to directly drive the vehicle
as well as the generator.
HV Battery
Supplies electric power to the MG2 during start-off, acceleration, and uphill
driving; recharged during braking or when the accelerator pedal is not
depressed.
InverterA device that converts the high-voltage DC (HV battery) into AC (MG1 and
MG2) and vice versa (Converts AC into DC).
Converter
Drops the high-voltage direct current (DC 273.6 V) into DC12 V in order to
supply electricity to body electrical components, as well as to recharge the
auxiliary battery (12 V).
HV (Hybrid Vehicle
Control) ECU
Information from each sensor as well as from the ECU (ECM, Battery ECU,
ABS ECU) is received, and based on this the required torque and output power
is calculated.
The HV ECU sends the calculated result to the actuators and controllers.
ECMSends a throttle open command to the electronically-controlled throttle in
accordance with the engine output request factor received from the HV ECU.
Battery ECUMonitors the charging condition of the HV battery.
Brake ECU
Controls the regenerative brake that is effected by the MG2 and the hydraulic
brake so that the total braking force equals that of a conventional vehicle that
is equipped only with hydraulic brakes.
Also, the brake ECU performs the ABS control conventionally.
Accelerator PedalConverts the accelerator angle into an electrical signal and outputs it to the HVAccelerator Pedal
Position Sensor
Converts the accelerator angle into an electrical signal and outputs it to the HV
ECU.
Shift Position SensorConverts the shift lever position into an electrical signal and outputs it to the
HV ECU.
SMR (System Main
Relay)Connects and disconnects the high-voltage power circuit through the use of
a signal from the HV ECU.
Service plugShuts off the high-voltage circuit of the HV battery when this plug is removed
for vehicle inspection or maintenance.

THS (TOYOTA HYBRID SYSTEM)
Shift Position
Sensor
182TH05
Accelerator
Pedal Position
Sensor
BRAKE
ECU
Shift Position
(Main and Sub)
Accelerator Angle
(Main and Sub)
Regenerative
Request FactorHV ECUInverter
Voltage
SMR Control
MG2MG1
RPMEngine
Power
RequestCharging
Condition,
Amperage
SMRSMR
Amperage
HV
Battery Engine
Planetary Gear
Unit
Wheel
Wheel
ECM
Battery
ECU
Hydraulic
Brake
Actual
Regenerative
Braking Factor
Auxiliary
Battery
Mechanical Power Path
Electrical Signal Hydraulic
Converter
25

SYSTEM DIAGRAM

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)
M-UU,
VU, WU
M-SDOWN
G-UU,
VU, WU
CONT 3
SENSORS ACTUATORS
INVERTER (for MG1)
INVERTER (for MG2)
G-SDOWN
DATA LINK CONNECTOR 3 SIL, TC
IGCT RELAYAUXILIARY
BATTERY MRELBATT
BATTERY ECU
ABS ECU
VEHICLE SPEED SIGNAL
(for Hybrid Transaxle)
ACCELERATOR PEDAL
POSITION SENSOR
SHIFT POSITION SENSOR
CRUISE CONTROL SWITCH
AIRBAG SENSOR ASSEMBLY
CIRCUIT BREAKER SENSOR
INTERLOCK SWITCH
(for Inverter Cover and Service Plug)
STOP LIGHT SWITCH
A / C ECU
CONVERTER NODD
MG2
M-REF,
SIN, COS
MG1
G-REF,
SIN, COS
ECM
COMBINATION METER

Vehicle Speed Signal SPD
INVERTER
(for MG1)
INVERTER
(for MG2)
CONT 2
SYSTEM MAIN RELAY NO.1
SYSTEM MAIN RELAY NO.2
SYSTEM MAIN RELAY NO.3
G-MOTT
M-MOTT
CONT 1
HV ECU
HTD, DTH
HTB, BTH
VPA1, 2
SFT, P, R,
N, D, B
CCS
ABFCS
ACS
ILK
STP EGON
HTE, ETH
ACON
G-INVT
G-IU, IV, IW
M-SINV, FINV
M-INVT
M-IU, IV, IW
GO
SPDO
ESTP
IB
G-SINV, FINV
MG1
MG2
28
2. Construction
The configuration of the THS control system in the Prius is shown in the following chart.

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)
182TH33
31
± REFERENCE ±
The MG1 and the MG2 are generally shut down when the shift lever is in the N position.
However, the shut-down function is canceled under the following exceptions:

During driving, if the brake pedal is depressed and a wheel locks up, the ABS is activated. After this, low
torque is requested from the MG2 to provide supplemental power in order to restart the rotation of the wheel.
Even if the shift lever is in the N position at this time, the shut-down function is canceled to allow the wheel
to rotate. After the wheel rotation has been restarted, the system resumes its shut-down function.

When the vehicle is driven in the D or B position and the brake pedal is depressed, the regenerative brake
operates. At this time, as the driver moves the shift lever to the N position, the brake hydraulic pressure in-
creases while the request torque of the regenerative brake decreases gradually so as not to create a sluggish
brake feel. After this, the system effects its shut-down function.
When any of the conditions described below is pres-
ent, the message prompt as shown appears in the
multi information display, accompanied by the illu-
mination of the master warning light and the continu-
ous sounding of the buzzer.

The ªREADYº light is illuminated, the shift lever
is in the N position, and the HV battery is dis-
charged.

The ªREADYº light is illuminated, the shift lever
is in the N position, and the driver's door is open.

The ªREADYº light is illuminated, the parking brake is engaged, the shift lever is in the B or D position, and
the driver's door is open.

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.