2001 TOYOTA PRIUS Service Repair Manual

THS (TOYOTA HYBRID SYSTEM)
182TH12
SOCExample of change in SOC
Upper SOC control limit
Control regionTarget SOC
control
Lower SOC control limit
Time
Overcharged region
Overcharged region
39
1. Battery ECU
The battery ECU provides the following functions.
SOC (state of charge) Control
While the vehicle is in motion, the HV battery
undergoes repetitive charging / discharging
cycles, as it becomes discharged by the MG2
during acceleration and charged by the regenera-
tive brake during deceleration. The battery ECU
outputs charge / discharge requests to the HV
ECU so that the SOC can be constantly main-
tained at a center level, by estimating the charg-
ing / discharging amperage.
Cooling Fan Control
To ensure the HV battery's performance considering the heat that is generated in the HV battery during
charging and discharging, the battery ECU controls the operation of the cooling fan.
HV Battery Malfunction Monitoring
This function includes the monitoring of the temperature and the voltage of the battery via the battery ECU.
If a malfunction is detected, the battery ECU protects the HV battery by restricting or stopping the charging
and discharging of the HV battery. In addition, this function illuminates the warning light, outputs DTCs
(Diagnostic Trouble Codes), and stores them in memory. For further details on the DTCs, refer to the 2001
Prius Repair Manual (Pub No. RM778U).

THS (TOYOTA HYBRID SYSTEM)
182TH11
HV Battery
SMR 2
SMR 1
Battery Module
(7.2 V x 19)
Resistor
Service Plug
High-Voltage Fuse
Battery Module
(7.2 V x 19)
SMR 3
182TH30
Service Plug 40
2. SMR (System Main Relay)
The SMR is a relay that connects and disconnects
the power source of the high-voltage circuit upon
receiving a command from the HV ECU. A total
of 3 relays, one for the negative side, and two for
the positive side, are provided to ensure proper op-
erations.
At the time of connection, SMR1 and SMR3 are
turned ON; after this, SMR2 is turned ON and
SMR1 is turned OFF. By allowing the controlled
current via the resistor to pass through initially in
this manner, the circuit is protected against rush
current.
At the time of disconnection, SMR2 and SMR3
are turned OFF in that order, and the HV ECU ver-
ifies that the respective relays have been properly
turned OFF.
3. Service Plug
By removing the service plug before performing any inspection or service, the high-voltage circuit is shut
off at the intermediate position of the HV battery, thus ensuring safety during service.
The service plug assembly contains a reed switch for interlock. Lifting the clip lock up turns OFF the reed
switch, which shuts off the SMR. However, to ensure safety, make sure to turn OFF the ignition switch before
removing the service plug. For further details on how to handle the service plug, refer to the 2001 Prius Repair
Manual (Pub No. RM778U). The main fuse for the high-voltage circuit is provided inside of the service plug
assembly.

THS (TOYOTA HYBRID SYSTEM)
182TH20
Cooling FanAir Intake
HV Battery Exhaust Duct No.2Exhaust Duct No.141
HV BATTERY COOLING SYSTEM
DESCRIPTION
When the temperature of the HV battery rises, the battery ECU executes a command to cause the cooling fan
to operate from OFF to LO, MID and HI speeds. However, if the air conditioning is being used at that time
to cool the vehicle's interior, and if there is still some margin left in the temperature of the HV battery, the
battery ECU keeps the fan OFF or running at LO speed, thus giving priority to the air conditioning.
The air intake for the cooling fan is located above the package tray trim. If an object (such as clothing) is
placed over this area, the HV battery might not be able to cool sufficiently, which could cause the output con-
trol warning light to illuminate.
CONSTRUCTION
This system feature a cooling fan which is driven by DC motor.

Specifications 
TypeSirocco Fan
Fan Size Dia x H mm (in.)100 x 40 (4.0 x 1.6)
Motor TypeDC Motor
Lo50
Air Flow Volume m3/hMid100
Hi150
Power Consumption W60
The operation of the cooling fans is controlled by the signals that are output by the battery ECU, which
monitors the temperature of the HV battery.

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.

CHASSIS ± P111 HYBRID TRANSAXLE
CHASSIS
182CH01
MG (Motor Generator) 2Power Splitting Device
MG (Motor Generator) 1
Transaxle Damper
Differential Oil Pump79
P111 HYBRID TRANSAXLE
DESCRIPTION
The P111 hybrid transaxle has been newly developed for the hybrid system application.
Containing a MG (Motor Generator) 2 for driving the vehicle and a MG (Motor Generator) 1 for generating
electrical power, the P111 hybrid transaxle uses a continuously variable transmission mechanism with power
splitting device that achieve smooth and quiet operation.

Specifications 
Pl t
The No. of Ring Gear Teeth78
Planetary
GearThe No. of Pinion Gear Teeth23Gear
The No. of Sun Gear Teeth30
Gear Ratio3.905
Number of Links74
ChainDrive Sprocket39
Driven Sprocket36
Counter GearDrive Gear30Counter GearDriven Gear44
Final GearDrive Gear26Final GearDriven Gear75
Fluid Capacity Liters (US qts, Imp.qts)4.6 (4.9, 4.0)
Fluid TypeATF Type T-IV or equivalent

CHASSIS ± P111 HYBRID TRANSAXLE
182CH02
Power Splitting Device
Transaxle
Damper
MG2
Sun Gear
Carrier
Ring GearMG1
Oil Pump
Silent ChainEngine
Counter Gears
Final Gears
182CH03
Coil Spring
Drive force
from the
engine 80
TRANSAXLE UNIT
1. General
The transaxle unit consists primarily of a transaxle damper, MG (Motor Generator) 1, MG2, power splitting
device and a reduction unit (containing a silent chain, counter gears, and final gears).
2. Transaxle Damper

A coil-spring type damper with low-twist char-
acteristics has been adopted as the mechanism
to transmit the drive force from the engine.

A torque fluctuation absorbing mechanism that
uses a dry-type single-plate friction material
has been adopted.