Abs/Traction Control System: Operation

When either rear tire begins slipping during acceleration, TRAC system pulses the rear brakes and throttles back the engine to regain traction. The driver has the option of activating or deactivating TRAC system. Located on the instrument panel is a TRAC OFF switch and TRAC indicator light.

Pressing the TRAC OFF switch turns off TRAC system. Press TRAC OFF switch again turns on TRAC system. TRAC system is always operative after engine start. When TRAC system is operative, the TRAC indicator light blinks. When a malfunction occurs and ABS/TRAC ECU sets a diagnostic mode, this light blinks self-diagnostic results.

An actuator is fitted to the throttle body. The TRAC actuator controls sub-throttle valve according to signals from ABS/TRAC ECU, thus controlling the engine output.

Sensors fitted to the sub-throttle valve shaft convert the opening angle to voltage signal and send signal to ABS/TRAC ECU via engine and transmission ECU, controlling throttle position signals.

The TRAC system brake actuator consists of a pump and accumulator assembly which produces regulated fluid pressure in the disc brake calipers of the right and left rear wheels separately. This function is also controlled by signals from the ABS/TRAC ECU.

Brake fluid pressure in the right and left rear wheels is controlled separately in three control modes (pressure increase, holding and pressure reduction). This process is controlled by solenoid valves, pressure switches and sensors.

If a malfunction occurs while the TRAC system is inoperative, the ECU immediately turns off the TRAC throttle relay, TRAC motor relay and TRAC brake main relay.

If malfunction occurs while TRAC is operative, the ECU continues control (stops the control or fully opens the sub-throttle valve depending on the types of malfunction). If TRAC becomes inoperative, the engine and brake systems operate like vehicles without TRAC regulated. The ECU continues normal control even when a malfunction occurs.