2001 TOYOTA PRIUS light

CHASSIS ± SUSPENSION AND AXLES
No.2 Trailing
Arm Bushing
182CH35
Axle Beam
Trailing ArmNo.1 Trailing Arm
BushingToe-Control Link
Trailing Arm
No.2 Trailing Arm
Bushing
No.3 Trailing Arm Bushing
181CH35
Lengthwise ForceLateral Force
Lateral Force
Applied to
the Toe
Control Link
Bushing
Movement
Lateral Force
Toe Control
Links
Left-Side
WheelLeft-Side
Wheel97
Trailing Arm and Axle Beam

Trailing arms that are lightweight, highly rigid, hollow inside, and a gently curved axle beam with a rear-
open U-shaped cross section have been adopted.

A toe control links integrated axle beam has been adopted. The toe control link consists of the No.1, No.2,
and No.3 trailing arm bushings, and it rotates within the horizontal plane of the vehicle, around the No.3
bushing that serves as the axial center.

The rolling regidity has been optimized through the adoption of the stabilizer bar.
Toe-Correct Function
The longitudinal and lateral forces that are created in the vehicle during cornering causes the toe control
links in the trailing arms to become deformed.
On a right turn, the right trailing arm moves forward and the left trailing arm moves rearward, creating a
tendency for the left wheel to toe out.
In this situation, the toe control links that are installed in the trailing arms are designed to utilize the lateral
force, which is applied to the toe control links during cornering, to correct the left trailing arm towards the
toe-in direction.
As a result, excellent stability and controllability are realized.

CHASSIS ± BRAKES
182CH39
182CH40
101

Specifications 
Master CylinderTypeSingleMaster CylinderDiameter mm (in.)22.22 (0.87)
Brake Booster TypeHydraulic
TypeVentilated Disc
Front BrakeCaliper TypePE54Front BrakeWheel Cylinder Dia. mm (in.)54.0 (2.13)
Rotor Size (D x T)* mm (in.)255 x 22 (10.04 x 0.87)
TypeLeading-Trailing Drum
Rear BrakeWheel Cylinder Dia. mm (in.)20.64 (0.81)
Drum Inner Dia. mm (in.)200 (7.87)
Brake Control Valve TypeP & B Valve
TypeDrum
Parking BrakeSize mm (in.)200 (7.87)g
Lever TypePedal
ABS with EBDSTD
*: D: Outer Diameter, T: Thickness
FRONT BRAKE
The PE54 type brake calipers and ventilated disc
rotor have been adopted. These brake calipers are
lightweight and compact to realize excellent brake
performance.
REAR BRAKE
General
The leading-trailing type drum brakes using
drums with a 200 mm (7.87 in.) inner diameter
have been adopted.
A hydraulic system that adjusts the clearance
between the shoes and the drum has been
adopted.

CHASSIS ± BRAKES105
4. Function of Main Components
ComponentsFunction
ABS Warning
LightLights up to alert the driver when the brake ECU detects the
malfunction in the ABS.
Combination
Meter
Brake System

Lights up together with the ABS warning light to alert the driver
when the brake ECU detects the malfunction not only in the ABS
but also in the EBD controlBrake System
Warning Lightbut also in the EBD control.

Lights up to alert the driver when the malfunction occurs in the
brake system.
Stop Light SwitchDetects the brake depressing signal.
Brake Warning BuzzerEmits a continuous sound to inform the driver that the ABS ECU
detects the malfunction in the hydraulic brake booster.
Speed SensorsDetect the wheel speed of each of the four wheels.
Brake ECU

Processes various sensor signals, regenerative brake signals, to
execute control of the ABS control, EBD control, regenerative
coordination control and hydraulic brake booster.

Communicates control data with the HV ECU.
HV ECUMaintains serial communication with the brake ECU to exchange
regenerative coordination control signals.
Hydraulic Brake Booster
Assists with the pedal effort applied to the brake pedal.

Supplies hydraulic pressure.
Brake ActuatorControls the brake fluid pressure to each brake wheel cylinder by
signals from the brake ECU.
Solenoid RelaySupplies power to the ABS's solenoid valve's in the brake actuator.
Pump Motor RelaysControl the pump motor operation in the hydraulic brake booster.

CHASSIS ± BRAKES
152CH17 182CH47
Reservoir Tank
Accumulator
Check
Valve
Pump and
Pump Motor To Master
Cylinder and
Solenoid
Valves
Pressure
Switch
PL
Relief
Valve
Pressure
Switch
PH
Brake ECUPump Motor
Relays
Brake Warning
BuzzerBrake System
Warning LightAccumulator
Pressure
Pressure
Switch PH
Pressure
Switch PLON
OFF
OFF
Time
Pump
Motor
Relief
ValveOpen
CloseBrake System
Warning Light
and Brake
Warning Buzzer
ON
OFF
ON
OFF
108
Hydraulic Brake Booster
1) General
Due to installation space constraints, a type of hydraulic brake booster that comprises two separate por-
tions has been adopted: the power supply portion (pump, pump motor, accumulator, pressure switches,
and relief valve) and the master cylinder portion.
Consisting of an pump and pump motor, accumulator, and hydraulic pressure switches, the hydraulic
brake booster performs the functions of both the booster and the master cylinder.
By optimizing the hydraulic circuits, the hydraulic pressure that is generated by the booster is applied
directly to the rear brakes. Thus, the hydraulic pressure from the master cylinder is used exclusively by
the front brakes.
2) Pump and Pump Motor, Accumulator, Pressure Switches and Relief Valve
If the accumulator pressure becomes lower than the pressure that is specified in the pressure switch PH,
which is used for detecting high pressure, the pressure switch PH turns OFF. Then, the brake ECU turns
ON the pump motor relays to operate the pump motor and the pump.
The brake fluid that is discharged by the pump passes through the check valve and is stored in the accumu-
lator. The hydraulic pressure that is stored in the accumulator is used for providing the hydraulic pressure
that is needed for normal braking, for operating the ABS, and for operating the EBD control, and for re-
generative brake cooperative controlling.
If the accumulator pressure becomes higher than the pressure that is specified in the pressure switch PH,
the pressure switch PH turns ON. Then, after several seconds, the brake ECU turns OFF the pump.
At this time, if the pressure switch PH malfunctions and causes the pump to operate continuously, the
relief valve opens to prevent excessive pressure from being generated.
Moreover, if the accumulator pressure becomes lower than the pressure that is specified in the pressure
switch PL, which is used for detecting low pressure, the pressure switch PL turns OFF. As a result, the
brake system warning light turns ON and the brake warning buzzer activates.
At this time, the ABS or EBD is prohibited from operating.

CHASSIS ± BRAKES
182CH55
Speed Sensors
Combination Meter
Speedometer
ABS Warning Light
Brake System Warning
Light
Brake Warning Buzzer
Stop Light Switch
ECM
HV ECU
Inverter
Battery ECU
Brake
ECU
Solenoid Relay
Motor Relay
Brake Actuator
ABS Solenoid
Valves
Switching Solenoid Valve
Linear Solenoid Valve
Master Cylinder Pressure
Sensor
Regulator Pressure Sensor
Front Wheel Pressure Sensor
Rear Wheel Pressure Sensor
Pump Motor
High Pressure Switch
Low Pressure Switch
Reservoir Level Switch
Hydraulic Brake Booster11 5
Brake ECU
1) General
Based on the signals received from the sensors the communication it maintains with the HV ECU, the
brake ECU effects conventional brake control, ABS with EBD control, and regenerative brake coopera-
tive control.
2) Fail Safe
If a malfunction occurs in the brake ECU, in the input signals from the sensors, or in actuator system,
this function prohibits the current from flowing to the brake actuator.
As a result, the solenoids in the brake actuator turn off, enabling the braking force of the hydraulic brake
to take effect. Furthermore, by illuminating the ABS warning light or the brake system warning light,
this function alerts the driver that a malfunction exists in the system.
Only if the regenerative brake system cannot be used, such as in the case of a malfunction in the commu-
nication with the HV ECU, this function switches controls to enable the hydraulic brake to generate the
entire brake force.
3) Warning Light Check Function
The ABS warning light and brake system warning light turns on for about 3 seconds after the ignition
switch is turned on to check the circuit.

CHASSIS ± BRAKES
182CH79
Port A
Pressure
Holding
Valve
To
Wheel
Cylinder
Port B
Pressure
Preduction
ValveTo
Reservoir
and Pump
From Wheel Cylinder
182CH80 182CH81
11 6
4) Self-Diagnosis
If the brake ECU detects a malfunction in the brake system, the ABS warning light and brake system
warning light will light up and alert the driver that a malfunction has occurred. The ECU will also store
the codes of malfunctions. See the 2001 Prius Repair Manual (Pub. No. RM778U) for the DTC (Diagnos-
tic Trouble Code) check method, DTC and DTC clearance.
Brake System Control
1) ABS with EBD control
a. General
The EBD control utilizes ABS, realizing the proper brake force distribution between front and rear
wheels in accordance with the driving conditions. In addition, during cornering braking, it also controls
the brake forces of right and left front wheels, helping to maintain the vehicle stability.
The distribution of the brake force is performed under electrical control of the brake ECU, which pre-
cisely controls the brake force in accordance with the vehicle's driving conditions.
b. Operation
Based on the signals received from the 4 wheel speed sensors, the brake ECU calculates each wheel
speed and deceleration, and checks wheel slipping condition. And according to the slipping condition,
the ECU controls the solenoid valves in order to adjust the fluid pressure of each wheel cylinder in the
following three modes: pressure reduction, pressure holding and pressure increase modes.
Not Activated
Normal Braking±±
ActivatedPressure Increase ModePressure Holding ModePressure Reduction Mode
Hydraulic
Circuit
Pressure
Holding Valve
(Port A)OFF
(Open)ON
(Close)ON
(Close)
Pressure
Reduction Valve
(Port B)OFF
(Close)OFF
(Close)ON
(Open)
Wheel Cylinder
PressureIncreaseHoldReduction

CHASSIS ± STEERING
182CH95
182CH76
Twist Angle
Basic Position
Cornering
Torque
[V]
Voltage
Voltage difference between
outputs 1 and 2 during
straight line driving (0)
Torque Sensor 2
Torque Sensor 1
0 ±+
Right Turn Left Turn127
ii) Steering to the right
When the driver turns the steering to the
right, the steering torque is transmitted to
the pinion shaft's input shaft, causing the
input shaft to rotate. Because the reaction
force of the ground surface acts on the rack
bar, the torsion bar that links the input shaft
and the pinion twists until a torque that
equalizes with the reaction force is gener-
ated. Thus, a relative displacement is
created between the resistor that is secured
onto the input shaft and the contact that is
secured onto the pinion shaft's output shaft.
As a result, the resistance changes, causing
the torque sensor's outputs 1 and 2 to
change as shown in the right diagram. The
EMPS ECU uses this voltage difference to
calculate the power assist torque to drive
the DC motor, thus generating a power as-
sist force in the pinion shaft via the reduc-
tion mechanism.
iii) Steering Hold Condition
The torsion bar shift to a position in which the sum of the driver's steering torque and the motor's assist
torque equalizes with the reaction force of the ground surface in order to maintain the steering holding
condition.
EMPS ECU
1) EMPS Control
The EMPS ECU receives signals from various sensors, judges the current vehicle condition, and deter-
mines the assist ampere to be applied to the DC motor accordingly.
2) Self-Diagnosis
If the EMPS ECU detects a malfunction in the EMPS system, the warning light that corresponds to the
function in which the malfunction has been detected lights up to alert the driver of the malfunction.
The EMPS ECU will also store the codes of the malfunctions. The DTCs (Diagnostic Trouble Codes)
can be accessed through the use of a hand-held tester. For details, see the 2001 Prius Repair Manual (Pub.
No. RM778U).
3) Fail-Safe
If the EMPS ECU detects a malfunction in the EMPS system, the system basically turns OFF the power
to prohibit power assist. As a result, the EMPS system operates the same way as manual steering.
However, depending on the location in which the malfunction occurred, power assist may be provided
by reducing the power assist amperage or by fixing the amount of power assist without relying on the
vehicle speed.

BODY ± BODY STRUCTURE
BODY
182BO01
: High Strength Sheet Steel 130
BODY STRUCTURE
DESCRIPTION
The Prius has adopted a body construction that achieves both high rigidity and safety.
LIGHTWEIGHT AND HIGHLY RIGID BODY
1. High Strength Sheet Steel
High strength sheet steel has been used in order to ensure body rigidity and realize a lightweight body.