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 noise 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 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 so 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 can return the fluid to the master cylinder.

If during the pressure hold or the pressure decrease mode the EBCM/EBTCM senses that the wheel speed returns to normal or increases, the EBCM/EBTCM 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.

Traction Control System (TCS)

The TCS is designed to limit wheel slip during acceleration when one or more of the drive wheels are accelerating too rapidly and the brake switch is off. The EBTCM monitors wheel speed slip through the ABS wheel speed sensors then processes wheel speed sensor data and sends a desired wheel torque value to the Powertrain Control Module via a Class 2 Serial Data Line signal. 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, thus improving the vehicle traction. Closing the TCS master cylinder isolating 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 can deactivate the TCS, if desired. In order to deactivate the TCS with the engine running, depress the Traction Control switch. The TRAC OFF Indicator in the Driver Information Display will illuminate. The system remains deactivated until the ignition switch is cycled, or the switch is pressed again. The TCS will be disabled under the following conditions:

Tires with ABS/TCS/TIM

The compact spare tire rotates faster than the standard tires that are original equipment. The EBCM/EBTCM compensates for this faster rotation but a DTC C1245 will set and Low Tire Indicator will illuminate until the tire is repaired or replaced then the RESET switch (located in the fuse panel) must be pushed to reset the Tire Inflation Module (TIM) system that is part of the EBCM/EBTCM. Refer to Tire and Wheel Specifications in Tire and Wheels for information on replacement tires.

The red BRAKE Indicator in the instrument cluster will illuminate to warn the driver of conditions in the brake system which 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 (closed is when the Brake fluid is low in the master cylinder reservoir). When the Brake fluid level switch is closed (low condition) a DTC C1247 is set in the EBTCM. The BRAKE warning Indicator will stay illuminated until the condition has been repaired.

ABS Indicator

The ABS indicator is located in the instrument cluster and will illuminate if a malfunction in the ABS is detected by the Electronic Brake Traction Control Module (EBCM/EBTCM). The ABS indicator informs the driver that a condition exists which results in turning off the antilock brake and traction control function. 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. Refer to Brake System Testing in Hydraulic Brakes. Conditions for the ABS indicator to turn on are as follows:

The TRAC OFF indicator located in the Driver Information Display will illuminate to notify the driver of the following:

As a bulb check procedure, the EBTCM will command the TRAC OFF indicator on for 3 seconds when the EBTCM receives Ignition power.

The LOW TRAC indicator is located in the Driver Information Display. The LOW TRAC indicator will illuminate to alert the driver of a low traction situation and to inform the driver the TCS is operating. It does not operate during ABS operation. The LOW TRAC indicator will remain on for approximately 3 to 4 seconds after the TCS event is complete.

As a bulb check procedure, the EBTCM will command the LOW TRAC indicator on for approximately 3 to 4 seconds when the EBTCM receives Ignition power.