System Operation; Traction Control Operation - Toyota Camry 1999 Electrical Troubleshooting Manual

ABS AND TRACTION CONTROL
SYSTEM OUTLINE
(ABS)
ABS is a brake system designed for the purpose to improve the operating ability securing the stability of the vehicle by
preventing the looking–up of the vehicle controlling the wheel cylinder pressure of all the four wheels at the time of sudden
braking.
1. INPUT SIGNALS
(1) Speed sensor signal
The speed of the wheels is detected and input to TERMINALS FL+, FR+, RL+, and RR+ of the ABS and traction ECU.
(2) Stop light SW signal
A signal is input to TERMINAL STP of the ABS and traction ECU when brake pedal is depressed.

2. SYSTEM OPERATION

When the wheels are to be locked–up, the solenoid inside the actuator will be controlled by the signal from the ABS and
traction ECU and the brake fluid in the wheel cylinder will flow through the reservoir and reduce the hydraulic pressure.
While the ABS is in operation, as the ABS and traction ECU always outputs the operation signal to the pump inside the
actuator, brake fluid stored inside the reservoir will be suctioned up by the pump inside the actuator and returned to the
master cylinder.
When the hydraulic pressure of the wheel cylinder is decompressed or increased until the necessary hydraulic pressure, the
solenoid inside the actuator is controlled by the control signal from the ABS and traction ECU and as a result, hydraulic
pressure of the wheel cylinder will be closed at both routes of the master cylinder and reservoir sides and the hydraulic
pressure of the wheel cylinder will become to be in the holding condition.
If the increase of hydraulic pressure volume of the wheel cylinder becomes necessary, with the control signal from the ABS
and traction ECU, the solenoid inside the actuator will be controlled and become the same condition as usual and the brake
fluid of the master cylinder will be sent to the wheel cylinder and will increase the hydraulic pressure of the wheel cylinder. At
this time, in the case that the brake fluid stays left in the reservoir, it will be sucked up by the pump inside the actuator and
will be sent to the wheel cylinder.
Also, increasing speed of the hydraulic pressure is controlled by outputting the increasing and the said holding one after
another.
(Traction control)
Traction control system is designed to perform the engine output control by the fuel cut and hydraulic pressure control of
driving wheel brake and control the spinning of the driving wheels. By doing this, it improves starting acceleration and
operating ability of the vehicle securing the driving ability in accordance with the road surface condition.

3. TRACTION CONTROL OPERATION

Estimating the vehicle speed from the rear wheel speed, comparing it with the front, driving wheel speed and judging the grip
condition of the driving wheels. From the estimated vehicle speed, target speed of the driving speed will be set. When the
front, driving wheel speed exceeds the control starting speed, it judges that the tire slip is occurred and performs the fuel cut
cylinder number control and brake control and then adjust to make the front wheel speed become the traction control target
speed. Controlling of the traction control will be completed when the vehicle move onto the road where the driving wheels will
not have a tire slip or when the driver decelerate.
SERVICE HINTS
ABS MOTOR RELAY [R/B NO.3]
3–4 : Approx. 62 Ω
ABS SOL RELAY [R/B NO.3]
4–6 : Approx. 80 Ω
A9, A10 ABS SPEED SENSOR FRONT LH, RH
1–2 : 0.6 kΩ–2.5 kΩ
A15 (A), A16 (B), A17 (C) ABS AND TRACTION ECU
(B) 8–GROUND : Approx. 12 volts with the ignition SW at ON position
(B)11–GROUND : Continuity with the ignition SW on and the traction off SW on (Traction control off)
(B)16–GROUND : Approx. 12 volts with the brake pedal depressed
(A)15, (C) 9, (C) 10–GROUND : Always continuity
A25, A26 ABS SPEED SENSOR REAR LH, RH
1–2 : 1.2 kΩ–2.3 kΩ
T2 THROTTLE POSITION SENSOR
1–2 : 3.5 kΩ–5.0 kΩ