brake fluid TOYOTA CAMRY 2000 Service Repair Manual

62CHASSISÐBRAKES
 MASTER CYLINDER
As in the previous model, the lockheed and
lockheed type master cylinder is used on the models
without ABS, and the portless and lockheed type
master cylinder is used on the models with ABS.
The portless and portless type master cylinder is
used on the models with ABS & TRAC system.
 ABS
1. General
As in the previous model, the braking of each wheel is controlled by the following 3 modes: pressure reduction,
pressure holding, and pressure holding mode.
During ABS activation, the ECU controls the fluid pressure of each front left and right wheels independently while
the fluid pressure of rear left and right wheels is controlled simultaneously.
However, the ABS actuator has been changed as shown in the table below. In addition, the diagnostic codes have
alsom been changed.
For diagnostic code check method, diagnostic code and diagnostic code clearance, see the 1997 Camry Repair
Manual (Pub. No. RM503U).
The operation of the ABS is the same as that of the '96 Corolla.

Type of ABS Actuator
Model
NewPreviousTypeNewPrevious
NIPPONDENSO ABS
(TMC Produced Model) 2±Position Solenoid Valve Type
Actuator
The ECU and realy are separate.3±Position Solenoid Valve Type
Actuato
The ECU and relay are separate.
BOSCH ABS
(TMM Produced Model)2±Position Solenoid Valve Type
Actuator with ECU and Relay3±Position Solenoid Valve and
Mechanical Valve Type Actuator
with ECU and Relay

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4. Hydraulic Circuit
The hydraulic circuit of the Nippondenso and Bosch systems are the same.
5. Operation
The hydraulic system of the ABS has 4 circuits. Although the hydraulic circuit described below is 1 circuit, it is
applicable to other circuits as well.
During Normal Braking (ABS not activated)
During normal braking, the ABS is not activated
and the ECU does not send control signal. When the
brake pedal is depressed, the fluid pressure in the
master cylinder rises, brake fluid passes from port
A to port B, and then flows to the brake wheel
cylinder. When the brake pedal is released, brake
fluid returns from the brake wheel cylinder to the
master cylinder through port B to port A and the No.
1 Check Valve.

Condition of Each Valve and Pump Motor
Part Name
Signal from
ABS ECUOperation
Pressure
Holding ValveOFFPort AOpen
Pressure
Reduction
Valve
OFFPort DClosed
Pump MotorOFFRotating

Hydraulic Circuit

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During Normal Braking (ABS not activated)
1) Pressure Reduction Mode
When the wheel is about to lock, the control signal
from the ECU causes port A to close, port D to open,
thus engaging the pressure reduction mode.
At this time, the brake fluid flows from the wheel
cylinder, through ports C and D, to the reservoir,
reducing the wheel cylinder pressure. At the same
time, the brake fluid is pumped and returned to the
master cylinder.

Condition of Each Valve and Pump Motor
Part Name
Signal from
ABS ECUOperation
Pressure
Holding ValveONPort AClosed
Pressure
Reduction
Valve
ONPort DOpen
Pump MotorONRotating
2) Pressure Holding Mode
After the fluid pressure in the wheel cylinder is
reduced or increased to the required pressure, a
control signal fromt he ECU causes ports A and D
to close. As a result, the system engages in the
pressure holding mode to maintain the fluid
pressure in the wheel cylinder.

Condition of Each Valve and Pump Motor
Part Name
Signal from
ABS ECUOperation
Pressure
Holding ValveONPort AClosed
Pressure
Reduction
Valve
OFFPort DClosed
Pump MotorONRotating

Hydraulic Circuit

Hydraulic Circuit

68CHASSISÐBRAKES
3) Pressure Increase Mode
When the fluid pressure in the wheel cylinder needs
to be increased in order to apply more braking force,
a control signal from the ECU causes port A to open,
port D to close, thus engaging in the pressure
increase mode.
Accordingly, the circuit will be in the same state as
in normal braking, in chich the brake fluid is sent
from the master cylinder to the wheel cylinder to
increase the fluid pressure in the wheel cylinder.
The fluid pressure increase rate is controlled by
repetition of the pressure increase and pressure
holding mode.

Condition of Each Valve and Pump Motor
Part Name
Signal from
ABS ECUOperation
Pressure
Holding ValveOFFPort AOpen
Pressure
Reduction
Valve
OFFPort DClosed
Pump MotorONRotating

Hydraulic Circuit

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5. Function of Components
No.ComponentFunction
1Slip Indicator LightBlinks to inform the driver when the TRAC system is operated.
2TRAC OFF Indicator Light
Lights to inform the driver when the TRAC system is turned OFF by
the by the TRAC OFF switch. And, blinks to alert the driver when
the ECU detects the malfunction in the TRAC system.
3ECM
Sends signals to the ABS & TRAC ECU, such as the throttle
valve opening angle, specific volume of intake air signal, etc.
Controls the engine output and shift timing in accordance with
the fuel cutoff request and shift timing request that are output by
the ABS & TRAC ECU.
4ABS & TRAC ECU
Judges the vehicle driving condition based on signals from 4 speed
sensors and signals from ECM, and sends fuel cut and shift timing
demand signals to the ECM and brake control signal to the ABS &
TRAC actuator.
5ABS & TRAC Actuator
Controls the brake fluid pressure to each brake wheel cylinder
of the driving wheel (front wheel) by signals from the ABS &
TRAC ECU.
ABS & TRAC
Solenoid RelayDirects electricity to the solenoid valves in the actuator.
6ABS & TRAC
RelayPump Motor
RelayControls the pump motor operation in the actuator.
7Speed Sensors (Front and Rear)Detect the wheel speed of each of four wheels.
8Throttle Position SensorDetects the throttle valve opening angle.
9TRAC OFF SwitchTurns the TRAC system inoperative.

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b. Reservoir Cut Solenoid Valve
When the TRAC system is active, a signal from the ABS & TRAC ECU causes the reservoir to cut solenoid valve
to turn ON in order the circuit from the master cylinder to the pump.
The basic construction and operation are the same as those of the pressure reduction valve.
c. Pressure Regulator Valve
Regulates the brake fluid pressure regulated by the pump to a pressure level needed for TRAC control.
2) Hydraulic Circuit
*: Pressure regulator valve is assembled into the master cut solenoid valve, however, it is illustrated separately to
explain its operation.

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3) Operation
The hydraulic system of the TRAC system consists of the following 2 circuits; the front right and front left. Although
the hydraulic circuit described below is one circuit, it is applicable to other circuits as well.
a. During Normal Operation (TRAC System not Activated)
When the TRAC system is inactive, the ABS & TRAC ECU does not output any controls signals. Thus, all valves
are OFF.
Accordingly, pressing on the brake pedal causes the brake fluid to flow from the master cylinder to port A, port B,
No. 1 check valve, port C, and port D, thus applying fluid pressure to the wheel cylinder.
Also, releasing the brake pedal causes the brake fluid to flow from the wheel cylinder to port D, port C, No. 2 check
valve, port B, and port A, thus returning to the master cylinder.
Thus, the brakes operate in the normal brake mode.

Hydraulic Circuit

Condition of Each Valve and Pump Motor
Part Name
Signal from
ABS & TRAC ECUOperation
Master Cut Solenoid ValveOFFPort BOpen
Reservoir Cut Solenoid ValveOFFPort HClosed
Pressure Holding ValveOFFPort COpen
Pressure Reduction ValveOFFPort FClosed
PumpOFFStop

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b. During Vehicle Acceleration (TRAC System Activated)
When a front wheel slips during acceleration, the TRAC system controls the engine output and braking of the front
wheels to help preventing wheel slippage.
The brake fluid pressure applied to the right and left front wheels is controlled separately accordingly to 3 control
modes ( pressure increase, holding, and pressure reduction) as explained below.
i) Pressure Increase Mode
During sudden acceleration or driving on a slippery surface, if the front wheels start to slip, a control signal from the
ABS & TRAC ECU causes the ABS & TRAC actuator to control the valves and pumps as described below, to effect
the pressure increase mode.
When the master cut and reservoir cut solenoid valves turn ON, port B is closed, port H is open and the pump operates
at the same time.
Accordingly, the brake fluid will be suctioned up from the master cylinder through parts G and H.
Then the brake fluid that is pressurized by the pump will be applied to the wheel cylinder through C and D.
Also, the brake fluid that pressurized by the pump is regulated to a constant pressure by the pressure regulator valve.

Hydraulic Circuit

Condition of Each Valve and Pump Motor
Part Name
Signal from
ABS & TRAC ECUOperation
Master Cut Solenoid ValveONPort BClosed
Reservoir Cut Solenoid ValveONPort HOpen
Pressure Holding ValveOFFPort COpen

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ii) Pressure Holding Mode
When the fluid pressure in the wheel cylinder is increased or decreased to attain the required pressure, the ABS &
TRAC ECU sends a control signal to turn ON the pressure holding valve.
Then, the fluid pressure that is applied to the wheel cylinder is cut off to hold the fluid pressure in the wheel cylinder.

Hydraulic Circuit

Condition of Each Valve and Pump Motor
Part Name
Signal from
ABS & TRAC ECUOperation
Master Cut Solenoid ValveONPort BClosed
Reservoir Cut Solenoid ValveOFFPort HClosed
Pressure Holding ValveONPort CClosed
Pressure Reduction ValveOFFPort FClosed
PumpONRotating

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iii) Pressure Reduction Mode
When the fluid pressure in the wheel cylinder needs to be decreased, the ABS & TRAC ECU sends a control signal
to turn the pressure reduction valve ON, causing port F to open
Accordingly, the brake fluid in the wheel cylinder flows to ports E and F, reservoir, and pump, to reduce the fluid
pressure in the wheel cylinder.
The fluid pressure reduction rate is controlled by repetition of the pressure reduction and holding mode.

Hydraulic Circuit

Condition of Each Valve and Pump Motor
Part Name
Signal from
ABS & TRAC ECUOperation
Master Cut Solenoid ValveONPort BClosed
Reservoir Cut Solenoid ValveOFFPort HClosed
Pressure Holding ValveONPort CClosed
Pressure Reduction ValveONPort FOpen
PumpONRotating