Traction Control System: Operation

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

Pressing the TRAC Off 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 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 a voltage signal and sends signals to ABS/TRAC ECU via engine and transmission ECU, controlling throttle position signals.

The TRAC Brake Actuator consists of a pump and accumulator assembly which produces fluid pressure regulated in the disc brake cylinders 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.

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

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