ABS System Operation

System Operation

Normal Braking Mode:

Antilock Braking Mode
An ABS stop occurs when the EBCM determines that one or more wheels are about to lose traction during braking. During an ABS stop the EBCM commands hydraulic pressure reduction at the wheel brake that is about to lose traction. The EBCM activates the solenoid valve for the affected wheel brake hydraulic channel. The solenoid valve triggers the adjoining flow control valve which directs hydraulic pressure into a buffer chamber. The result is a reduction in hydraulic pressure at the wheel brake thus reducing the tendency of wheel slip.

When the wheel is no longer slipping the EBCM deactivates the solenoid valve. This action allows the flow control valve to increase hydraulic pressure at the wheel brake.

This operation continues for all wheels until the wheels are no longer slipping for the duration of the stop. Although the ABS can modulate hydraulic pressure to each wheel brake it cannot increase hydraulic pressure above the amount which is transmitted by the master cylinder during braking. The driver will notice a slight brake pedal pulsation during an ABS stop. This sensation is related to ABS component operation feedback and is considered normal.

System Self Test
The ABS performs a series of tests to the ABS components for proper operation and readiness. The initialization starts when the ignition switch is turned from the LOCK to the ON position. The EBCM turns ON the ABS indicator for 3 seconds. When the ABS indicator turns OFF a slight mechanical noise can be heard. This condition is normal. This noise comes from the BPMV assembly as the EBCM tests solenoid valves and the pump motor.

A slight pulsation may be felt when stepping on the brake pedal while the EBCM is testing the solenoid valves and the pump motor. This condition is considered normal brake pedal feedback.

ABS Indicator Operation
The ABS uses an indicator located in the instrument panel gauge cluster. When turning the ignition switch from the LOCK to the ON position the ABS indicator illuminates for three seconds. If the ABS is operating properly, the indicator turns OFF. If the ABS detects a malfunction, the indicator will stay ON to warn the driver that the ABS is disabled and it needs service.

Tires and ABS
Using the compact spare supplied with the vehicle will not affect the operation of the ABS. The ABS compensates for the smaller compact spare tire. However the driver will notice increased stopping distances due to the reduced size of the compact spare tire.

Replacement Tires
The tire size is important for proper performance of the ABS. When replacing the original tires use the following replacement guidelines:
^ Use a tire of the same size.
^ Use a tire of the same load range.
^ Use a tire with the same construction as the original tires.

Replace the tires in axle sets and only with tires of the same Tire Performance Criteria (TPC) specification number. Use of any other tire size or type may seriously affect the ABS operation.