When wheel slip is noted during a brake application, the ABS will enter the antilock mode. During antilock braking, the hydraulic pressure in the individual wheel circuits is controlled in order to prevent any wheel from slipping. A separate hydraulic line and specific solenoid valves are provided for each wheel. The ABS can decrease, hold, or increase the hydraulic pressure to each wheel brake. However, the ABS cannot increase the hydraulic pressure above the amount that the master cylinder transmits during braking. During antilock braking, a series of rapid pulsations will be felt in the brake pedal. The rapid changes in the position of the individual solenoid valves as they respond to the desired wheel speed causes the pulsations. This pedal pulsation is present during antilock braking and will stop when normal braking is resumed or when the vehicle comes to a stop. A ticking or popping nose may also be heard as the solenoid valves rapidly cycle. During antilock braking on dry pavement, the tires may make intermittent chirping noises as they approach slipping. These noises and pedal pulsations are normal during antilock operation. Brake pedal operation during normal braking should be no different than previous systems. Maintaining a constant force on the pedal provides the shortest stopping distance while maintaining vehicle stability.

The Dynamic Rear Proportioning (DRP) is a control system that replaces the hydraulic proportioning function of the combination valves in the base brake system. The DRP control system is part of the operation software in the EBCM. The DRP uses active control with existing ABS in order to regulate the vehicle's rear brake pressure.

DTC C1248 sets in order to indicate that the EBCM illuminated the red BRAKE warning indicator. The EBCM cannot perform DRP due to another fault in the ABS/TCS system. DTC C1248 will never set by itself.

When the EBCM senses the wheel slip, the EBCM closes the Inlet valve and keeps the Outlet valve closed in the BPMV in order to isolate the system. This holds the pressure steady on the brake so that the hydraulic pressure does not increase or decrease.

If during the pressure hold mode the EBCM still senses wheel slip, the EBCM will decrease the pressure to the brake. The Inlet valve is left closed and the Outlet valve is opened. The excess fluid is stored in the accumulator until the return pump can return the fluid to the master cylinder.

If during the pressure hold or the pressure decrease mode the EBCM senses that the wheel speed is too fast, the EBCM will increase the pressure to the brake. The Inlet is opened and the Outlet valve is closed. The increased pressure comes from the master cylinder and is related to the pressure applied to the brake pedal.

The TCS is designed to limit wheel slip during acceleration when one or more of the drive wheels are accelerating too rapidly. Traction control will not have any effect on vehicle operation until the electronic brake control module (EBCM) detects one or both of the front wheels rotating faster than the rear wheels. The TCS accomplishes this by two methods, engine torque reduction and brake intervention. The two methods are used together to control wheel slip during acceleration. Both methods are described below.

The Vehicle Stability Enhancement System (VSES) includes an additional level of control to the EBCM. The VSES is also known as the Precision Control System (PCS) and the instrument cluster indicator lamp is labeled with the acronym PCS. The VSES monitors the wheel speeds and yaw/lateral accelerometer sensor inputs to calculate a desired yaw rate, and compare the inputs to the actual yaw rate reported by the yaw/lateral accelerometer sensor. Steering maneuvers can cause the desired yaw rate to differ from the reported yaw rate by some amount. This difference can result from tire compliance, suspension compliance and wheel slip. If the difference between desired and actual yaw rate is too large, the controller intervenes at appropriate wheels increasing or decreasing the braking pressure at these wheels. If wheel slip rates are excessive, traction control may activate to reduce engine power.

The red BRAKE warning indicator in the instrument cluster illuminates to warn the driver of conditions in the brake system which may result in reduced braking ability. The indicator stays illuminated until the condition has been repaired. The following conditions will cause the red BRAKE warning indicator to illuminate:

The ABS indicator is located in the instrument cluster and illuminates if a malfunction in the ABS is detected by the EBCM. The ABS indicator informs the driver that a condition exists which results in disabling ABS. If only the ABS indicator is on, normal braking with full power assist is available. If the BRAKE and ABS indicators are on, a problem may exist in the hydraulic brake system. The following conditions will cause the ABS indicator to illuminate:

Illumination of the BRAKE warning Indicator may indicate reduced braking ability and the disabling of the DRP system. Illumination of the ABS indicator without the BRAKE warning Indicator ON indicates only that ABS braking is no longer available. Power assisted braking without ABS control is still available. Refer to in Hydraulic Brakes for diagnosis of any condition which causes the BRAKE warning Indicator to illuminate.