brake fluid TOYOTA PRIUS 2001 Service User Guide

CHASSIS ± BRAKES
152CH25
Reaction RodTo
ReservoirFrom
Accumulator
Spool Valve
Regulator
From
Reservoir Tank
Power Piston
Rubber
Reaction
DiscOperating Rod
ªAº
ªBº
Return
Spring
To Rear
BrakeTo Front
BrakeReturn
Spring
Master Cylinder PistonBooster Chamber
152CH26
Reaction Rod
To
ReservoirFrom
Accumulator
Regulator
From
Reservoir Tank
Power Piston
Rubber
Reaction
Disc
Spool Valve
To Rear
BrakeTo Front
Brake
Master Cylinder PistonBooster Chamber 11 0
b. Operation
i) Pressure Increase (Low Pressure)
The pedal effort that is applied to the brake pedal is transmitted via the operating rod, power piston,
and master cylinder piston. However, because the load setting of the master cylinder's return spring
is higher than that of the regulator piston's return spring, the regulator piston gets pushed before the
volume in the master cylinder becomes compressed. As a result, the spool valve moves forward.
The spool valve closes the port ªAº between the reservoir and the booster chamber (behind the power
piston) and opens the port ªBº between the accumulator and the booster chamber. Then, the pressur-
ized brake fluid is introduced into the booster chamber to provide a power assist to the pedal effort.
When the pressure is introduced into the booster chamber, the power assist overcomes the force of the
master cylinder's return spring. This causes the volume in the master cylinder to become compressed
and increases the pressure that is applied to the front brakes. At the same time, the pressure in the boost-
er chamber increases the pressure that is applied to the rear brakes.
During the initial stage of the brake operation, the booster pressure that is applied to the rubber reaction
disc is small. Therefore, a return force in the rightward direction does not apply to the spool valve via
the reaction rod.
ii) Pressure Increase (High Pressure)
In contrast to the time when the pressure is low, when the pressure is high, the booster pressure that
is applied to the rubber reaction disc increases. Accordingly, the rubber reaction disc deforms and
causes a return force in the rightward direction to be applied to the spool valve via the reaction rod.
Therefore, in contrast to the time when the pressure is low, a greater reaction force is transmitted to
the brake pedal.
As a result, a variable servo mechanism is realized, in which the servo ratio is lower during high pres-
sure than during low pressure.

CHASSIS ± BRAKES
152CH29
From
Reservoir
To Front
Brake
182CH49
To Wheel Cylinders
From
Master
Cylinder
From Hydraulic
Brake Booster
To Front
Wheel
Cylinders
To Rear Wheel
Cylinders
SMC1 and SMC2 SS 11 2
v) During Power Supply Malfunction
If the accumulator pressure is affected due to some type of malfunction, no pressure will be supplied
by the regulator. Then, a power assist cannot be provided to the force that is applied via the brake pedal
and the pressure to the rear brakes cannot be increased.
The pressure to the front brakes will be increased by the master cylinder in accordance with the pedal
effort applied to the brake pedal.
Brake Actuator
1) Switching Solenoid Valves
The control signals from the brake ECU cause the valves to open and close to switch the passages of the
brake fluid. There are 3 switching solenoid valves (SMC1, SMC2, and SS) and they switch the passages
to effect conventional brake control and ABS control.

CHASSIS ± BRAKES
182CH50
To Wheel Cylinder From Hydraulic
Brake BoosterFrom Wheel
CylinderTo Reser-
voir Tank
Pressure Holding Valve
(SFRH, SFLH, SRrH)Pressure Reduction Valve
(SFRR, SFLR, SRrR)
From Hydraulic
Brake Booster
Pressure Holding
Valve
To Wheel
Cylinder
Pressure
Reduction
Valve
Increase HoldingFrom
Wheel
Cylinder
To Reservoir Tank
Decrease
182CH51
To Wheel Cylinders
From
Hydraulic
Brake
Booster
To Built-In Reservoir
From
Wheel
Cylinders
SLA SLR
11 3
2) ABS Solenoid Valves
The control signals from the brake ECU cause the valves to open and close to switch the passages of the
brake fluid. There are 2 (pressure holding valve, pressure reduction valve) ABS solenoid valves pro-
vided. The pressure increases if no current is applied to either valve. The pressure is held if current is
applied only to the pressure holding valve. The pressure decreases if current is applied to both the pres-
sure holding valve and pressure reduction valve. To effect control independently to the front wheels, si-
multaneously to both rear wheels, 6 solenoid valves are provided.
3) Linear Solenoid Valves
The control signals from the brake ECU cause the valves to open and close to regulate the volume of the
brake fluid that flows into the wheel cylinders. There are 2 types of linear solenoids, the SLA for pressure
increase and the SLR for pressure decrease, and they regulate the wheel cylinder pressure in accordance
with the fluctuations in the regenerative brake force. In addition, the SLA contains a relief function to
provide hydraulic pressure to the wheel cylinders in the event of a brake ECU failure.

CHASSIS ± BRAKES
182CH52
Spring
for 1st
Stage
Spring
for 2nd
StageTo
ReservoirStroke
Simulator
Full Stroke
Pedal Stroke 2nd Stage
Spring
Characteristics
1st Stage +
2nd Stage
Spring
Characteristics
Master Cylinder Hydraulic Pressure From
Master
Cylinder
182CH53
From wheel Cylinder (SLR)
182CH54
11 4
4) Stroke Simulator
The stroke simulator generates a pedal stroke in accordance with the driver's pedal effort during braking.
Containing 2 types of coil springs with different spring constants, the stroke simulator provides pedal
stroke characteristics in 2 stages in relation to the master cylinder pressure.
5) Reservoir
Temporarily stores the brake fluid to absorb
the pressure when regulating the wheel cylin-
der pressure.
6) Pressure Sensors
Mounted on the brake actuator, the pressure
sensor linearly detects the pressure that is gen-
erated in the master cylinder, regulator, and
the front and rear wheel cylinders and outputs
them to brake ECU.

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
182CH68
Rear Wheel
Speed SensorsBrake ECU
Torque Sensor Signal 1
Torque Sensor Signal 2
EMPS
ECUMeter ECU
Gateway ECUDLC3
Display ECU
Multi-information
Display
123
EMPS (Electric Motor-assisted Power Steering)
1. General
In accordance with sensor information such as that provided by the rear wheel speed sensors, the torque sen-
sor that is mounted on the steering gear, and the EMPS ECU determines the direction and the force of the
power assist and actuates the DC motor that is mounted on the steering gear to provide power assist to the
steering effort.
The EMPS in the Prius the following features:
This system can provide power assist even when the engine is stopped.
This system offers excellent fuel economy characteristics because power assist is provided by the DC mo-
tor that is mounted on the steering gear, and this motor consumes energy only when power assist is re-
quired.
Unlike the conventional hydraulic power steering system, this system excels in serviceability because it
does not require pipes or the power steering fluid.

System Diagram 

IN04Q±11
IN±46
± INTRODUCTIONTERMS
46 Author: Date:
2001 PRIUS (RM778U)
TERMS
ABBREVIATIONS USED IN THIS MANUAL
AbbreviationsMeaning
ABSAnti±Lock Brake System
ACAlternating Current
ACCAccessory
ACISAcoustic Control Induction System
ACSDAutomatic Cold Start Device
A.D.D.Automatic Disconnecting Differential
A/FAir±Fuel Ratio
AHCActive Height Control Suspension
ALRAutomatic Locking Retractor
ALTAlternator
AMPAmplifier
ANTAntenna
APPROX.Approximately
A/TAutomatic Transmission (Transaxle)
AT FAutomatic Transmission Fluid
AUTOAutomatic
AUXAuxiliary
AV GAverage
AV SAdaptive Variable Suspension
BABrake Assist
BACSBoost Altitude Compensation System
BATBattery
BDCBottom Dead Center
B/LBi±Level
B/SBore±Stroke Ratio
BTDCBefore Top Dead Center
BVSVBimetallic Vacuum Switching Valve
Calif.California
CBCircuit Breaker
CCoCatalytic Converter For Oxidation
CDCompact Disc
CFCornering Force
CGCenter Of Gravity
CHChannel
COMB.Combination
CPECoupe
CPSCombustion Pressure Sensor
CPUCentral Processing Unit
CRSChild Restraint System
CTRCenter
C/VCheck Valve
CVControl Valve

MA02G±02
MA±4
± MAINTENANCEUNDER HOOD
57 Author: Date:
2001 PRIUS (RM778U)
UNDER HOOD
GENERAL MAINTENANCE
1. GENERAL NOTES

Maintenance items may vary from country to country. Check the owner's manual supplement in which
the maintenance schedule is shown.

Every serice item in the periodic maintenance schedule must be performed.

Periodic maintenance service must be performed according to whichever interval in the periodic main-
tenance schedule occurs first, the odometer reading (miles) or the time interval (months).

Maintenance service after the last period should be performed at the same interval as before unless
otherwise noted.
2. WINDSHIELD WASHER FLUID
Check that there is sufficient fluid in the tank.
3. ENGINE COOLANT LEVEL
Check that the coolant level is between the ºFULLº and ºLOWº lines on the see±through reservoir.
4. RADIATOR AND HOSES
(a) Check that the front of the radiator is clean and not blocked with leaves, dirt or bugs.
(b) Check the hoses for cracks, kinks, rot or loose connections.
5. BRAKE FLUID LEVELS
Check that the brake fluid levels are near the upper level line on the see±through reservoirs.
6. CHECK TRANSAXLE OIL (FLUID)

Visually check the transaxle for oil (fluid) leakage.

If leakage is found, check for the cause and repair.
HINT:
Wait until the engine and motor cools down (approx. 30 min.) before checking the fluid level after extended
driving at high speeds, in hot weather, in heavy traffic or pulling a trailer.

PP16F±02
± PREPARATIONBRAKE
PP±41
2001 PRIUS (RM778U)
LUBRICANT
ItemCapacityClassification
Brake fluid±SAE J1703 or FMVSS No. 116 DOT 3

PP26E±02
PP±50
± PREPARATIONBODY ELECTRICAL
2001 PRIUS (RM778U)
EQUIPMENT
Voltmeter
Ammeter
Ohmmeter
Test lead
SyphonBrake fluid level warning switch
Bulb (3.4W)Fuel sender gauge, Fuel level warning switch
Dry cell batteryWireless door lock transmitter
Torque wrench
Masking tapeRear window defogger wire
Tin foilRear window defogger wire