Anti-Lock Brake System: Operation

In anti-lock braking mode (wheel speed signals indicate a wheel is about to lock-up), Hydraulic and Electronic Control Unit (HECU) decreases pressure as necessary to prevent wheel lock-up. This function continues as long as necessary during braking. During normal braking, HECU controls distribution of fluid pressure to front and rear wheels. This eliminates the need for a proportioning valve.

The ABS system also has a "failure" mode. When system detects a malfunction, the HECU disables anti-lock braking and allows normal braking only. System then stores Diagnostic Trouble Code (DTC) and illuminates ABS warning light. DTCs are retrieved for diagnosis using scan tool. See RETRIEVING & CLEARING DIAGNOSTIC TROUBLE CODES  under DIAGNOSIS & TESTING.

When drive wheel speed exceeds a given amount, the HECU determines that the drive wheels are slipping and outputs a signal to reduce engine power.