Anti-Lock Brake System: Operation: ECM

The ECM is located under passenger seat. During braking, ECM monitors rear wheel lock-up, based on input signals from speed sensor and brakelight switch. To prevent wheel lock-up, ECM controls hydraulic brake pressure to rear wheels by controlling ALV.

The ECM performs a self-check operation on anti-lock brake system every time ignition is turned on. The self-check operation activates isolation valve and dump valve (located in ALV) to check for defective operation.

If system is operating correctly, ANTI-LOCK indicator light on instrument panel will be activated for 2 seconds and then go off. If system is defective, ANTI-LOCK indicator light will remain on and a diagnostic code will be stored in ECM memory. Diagnostic code can be obtained to determine system failure. See RETRIEVING CODES under DIAGNOSIS & TESTING.

NOTE: If diagnostic code exists, BRAKE warning light will also be activated. In case ECM cannot shut down anti-lock brake system, ECM will melt an internal fuse to prevent system operation.