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 may decrease, hold, or increase the hydraulic pressure to each wheel brake. 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.

When the EBCM/EBTCM senses the wheel slip, the EBCM/EBTCM 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 in order to ensure that the hydraulic pressure does not increase or decrease.

If during the pressure hold mode the EBCM/EBTCM still senses wheel slip, the EBCM/EBTCM 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 returns the fluid to the master cylinder.

If during the pressure hold or the pressure decrease mode the EBCM/EBTCM senses that the wheel speed is too fast, the EBCM/EBTCM will increase the pressure to the brake. The inlet valve 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.

Traction control will not have any effect on vehicle operation until the control module detects one or both of the front wheels rotating faster than the rear wheels. At this time, the EBTCM will request the PCM to reduce the amount of torque applied to the drive wheels. The PCM retards the timing and turns off the supercharger (if equipped) and the fuel injectors. The EBTCM applies the front brakes in order to reduce the torque to the front wheels. Once the front wheels begin to rotate at the same speed as the rear wheels, the system will return full control to the driver. During the traction control mode, if the brake is applied to only one front wheel, most of the engine torque will be directed to the other front wheel. This improves the vehicle traction. Closing the TCS master cylinder isolation valve isolates the master cylinder from the rest of the system. The TCS prime valves open in order to allow the pump to get the brake fluid to build the pressure for braking. The drive wheel circuit solenoids are energized as needed in order to allow for pressure hold, pressure increase, or pressure decrease. The driver may deactivate the TCS, if desired. In order to deactivate the TCS with the engine running, depress the traction control disable switch. The TRACTION OFF indicator in the instrument cluster will illuminate. The system remains deactivated until the ignition switch is cycled, or the switch is pressed again.

The speed dependent steering system (Magnasteer) incorporates a controller into the EBCM/EBTCM. A Magnasteer DTC C1241 will not cause the ABS or TRACTION OFF indicators to turn on. Refer to Variable Effort Steering Description in Variable Effort Steering for more information.

The compact spare tire rotates faster than the others. The EBCM/EBTCM compensates for this faster rotation.

The tire size is important for the performance of the ABS/TCS. Ensure that the replacement tires are the same size load range and construction as the original tires. Replace the tires in axle sets and only with tires of the same tire performance criteria specification number. Use of any other tire size or type may seriously affect ABS/TCS operation.

The red BRAKE indicator in the instrument cluster will illuminate in order to warn the driver of conditions in the brake system that may result in reduced braking ability. The indicator will also illuminate when the parking brake is applied or not fully released, or if the brake fluid level switch is closed. The BRAKE warning indicator will remain illuminated until the condition has been repaired. Refer to Brake Warning Lamp Description in Hydraulic Brakes.

The ABS indicator is located in the instrument cluster and will illuminate if a malfunction in the ABS is detected by the EBCM/EBTCM. The ABS indicator informs the driver that a condition exists which results in turning off the ABS and TCS function. If only the ABS and TCS indicators are 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 may cause the ABS indicator to turn on:

Illumination of the TRACTION OFF indicator indicates that a malfunction has occurred and the TCS has been disabled, or the traction control switch has been pressed turning the system off.

Illumination of the TRACTION ACTIVE indicator indicates that traction control is active. This indicator does not indicate a malfunction has occurred or service is needed.