DSC DSC uses the brakes and powertrain torque control to help maintain the lateral stability of the vehicle. While the ignition is on the DSC function is permanently enabled unless selected off by the DSC switch. Even if DSC is deselected, driving manoeuvres with extreme yaw or lateral acceleration may trigger DSC activity to assist vehicle stability. DSC enhances driving safety in abrupt manoeuvres and in understeer or oversteer situations which may occur in a bend. The ABS module monitors the yaw rate and lateral acceleration of the vehicle, and the steering input, then selectively applies individual brakes and signals for powertrain torque adjustments to reduce understeer or oversteer. In general: in an understeering situation, the inner wheels are braked to counteract the yaw movement towards the outer edge of the bend; in an oversteering situation, the outer wheels are braked to prevent the rear end of the vehicle from pushing towards the outer edge of the bend. The ABS module monitors the tracking stability of the vehicle using inputs from the wheel speed sensors, the steering angle sensor and the yaw rate and lateral acceleration sensor. The tracking stability is compared with stored target data and, whenever the tracking stability deviates from the target data, the ABS module intervenes by applying the appropriate brakes. On vehicles with an automatic transmission, when the DSC function is active, the ABS module also signals the Transmission Control Module (TCM) to prevent gear shifts. If necessary, the ABS module also signals:
- The ECM, to reduce engine torque.
- The transfer box control module, to adjust the locking torque of the center differential.
- The rear differential control module, to adjust the locking torque of the rear differential. The DSC function overrides the differential locking torque requests from the terrain response system.
ETC ETC attempts to optimize forward traction by reducing engine torque or braking a spinning wheel until it regains grip. ETC is activated if an individual wheel speed is above that of the vehicle reference speed (positive slip) and the brake pedal is not pressed. The spinning wheel is braked, allowing the excess torque to be transmitted to the non spinning wheels through the drive line. If necessary, the ABS module also sends a high speed CAN bus message to the ECM to request a reduction in engine torque. Torque reduction requests are for either a slow or fast response: a slow response requests a reduction of throttle angle (4.0L and 4.4L only); a fast response requests an ignition cut-off (4.0L and 4.4L) or a fuel cut-off (2.7L Diesel). When the DSC function is selected off with the DSC switch, the engine torque reduction feature is disabled. On vehicles with an automatic transmission, when the ETC function is active the ABS module also signals the TCM to prevent gear shifts.
