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 senses 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 returns to normal or increases, 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.

Tires with ABS

The compact spare tire rotates faster than the standard tires that are original equipment. The EBCM compensates for this faster rotation until the tire is repaired or replaced. Refer to Tire Description 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), 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 Control Module (EBCM). The ABS indicator informs the driver that a condition exists which results in turning off the antilock brake 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: