Traction Control System: Operation

When either rear tire begins slipping during acceleration, TRAC pulses rear brakes and reduces airflow through throttle body to regain traction. The driver has the option of activating or deactivating TRAC. Located on the instrument panel is a TRAC cut switch and TRAC indicator light.

Pressing the TRAC cut switch turns TRAC off. Pressing TRAC Off again changes TRAC to on. TRAC is reset to on when engine is restarted. When TRAC system is on, the TRAC indicator light blinks. When a malfunction occurs and ABS/TRAC ECU sets a diagnostic code, this light blinks self-diagnostic results.

An actuator is fitted to 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 a voltage signal and send signals to ABS/TRAC ECU via Engine Control Module (ECM), controlling throttle position signals.

The TRAC brake actuator consists of a pump and accumulator assembly which produces fluid pressure regulated in the disc brake calipers of each rear wheel. This function is also controlled by signals from the ABS/TRAC ECU and TRAC ECU (throttle valve motor driver on LS400).

Brake fluid pressure to 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.

When a malfunction occurs, TRAC system becomes inoperative. The engine and brake systems operate normally. The ECU continues normal control even when a malfunction occurs.