TOYOTA CAMRY 2000 Service Repair Manual

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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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6. Construction and Operation of Components
TRAC OFF Switch and Indicator Light
1) TRAC OFF Switch
When pressing, this switch turns the TRAC system to be inoperative. Pressing it again changes it to be operative.
When turning the ignition switch from ªOFFº to ªONº, TRAC system always becomes operative.
2) TRAC OFF Indicator Light
This light comes on when the TRAC system is set inoperative by the TRAC OFF switch, and informs the driver
accordingly. And blinks to alert the driver when a malfunction has occurred in the engine and TRAC system.
3) Slip Indicator Light
When the TRAC system is operative, the light blinks and informs the driver accordingly.
ABS & TRAC Actuator
1) Construction
The ABS & TRAC actuator consists of 12 two±position solenoid valves, 1 motor, 2 pumps 2 reservoirs and 2 pressure
regulator valves.
The 12 two±position solenoid valves consists of 2 master cut solenoid valves, 2 reservoirs cut solenoid valves, 4
pressure holding valves, and 4pressure reduction valves.
Pressure regulator valve is assembled into the master cut solenoid valve.
The basic construction and operation of the pump, reservoir, pressure holding valve, and pressure reduction valve
are shared with ABS.
a. Master Cut Solenoid Valve
When the TRAC system is active, a signal from the ABS & TRAC ECU causes the master cut solenoid valve to turn
ON in order to shut off the circuit between the master cylinder and the front brake wheel cylinder.

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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

Pressure Reduction ValveOFFPort FClosed
PumpONRotating

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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

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ABS & TRAC ECU
1) Wheel Speed Control
The ABS & TRAC ECU constantly receives signals from 4 speed sensors and calculates the speed of each wheel and
vehicle speed.
During sudden acceleration or driving on a slippery surface, if the drive wheels (front wheels) start to slip, the
difference in speed between the drive wheels are slipping.
Then, the ABS & TRAC ECU executes the right and left independent control of the front wheel brakes, the engine
torque control through fuel cutoff, and shift timing control according to the extent of the slip.
TRAC operation processes are described below.
1. The vehicle speed is determined by way of the rear wheel speed. This speed is then compared to the speed of the
front wheels, which are the drive wheels, to determine the slip condition of the drive wheels (front wheels).
2. The target control speed for the drive wheels is set based on the estimated vehicle speed.
3. If the speed of the front wheels, which are the drive wheels, exceeds the control starting speed, the ABS & TRAC
ECU determines that a slip has occurred and cuts off fuel according to the number of cylinders. By executing
engine torque control and brake control in this manner, the system regulates the speed
so that front wheels attain the target control speed. In addition, the system executes control to
prohibit the shifting of the automatic transaxle at this
time.
4. TRAC control ends when the drive wheels move to non±slippery surface or when the driver releases the
accelerator pedal.

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2) Initial Check
An initial check is carried out once every a few seconds after the ignition was turned on. The functions of each
solenoid valve and pump motor in the actuator are checked on order.
3) Self±Diagnosis
If the ABS & TRAC ECU detects a malfunction in the engine, ABS or TRAC system, it blinks the TRAC OFF
indicator light to alert the driver of the malfunction. At the same, the ABS & TRAC 1997 Avalon Repair Manual
(Pub. No. RM504U) for the diagnostic code check method, diagnostic code and diagnostic code clearance.
4) Fail±Safe
In the event of a malfunction in the engine, ABS or TRAC system, the ABS & ECU prohibits the TRAC system.
Thus, the brake and engine controls will operate in the same conditions as those without the TRAC system.