Section 2 (Anti-Lock Brake System - 4WAL): Operation

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2001 GMC Savana Special, 2001 GMC Savana Camper Special, 2001 GMC Savana, 2001 Chevrolet Chevy Express, and 2000 GMC Savana Special. However, it is still accessible from the selected car via links, so may be relevant.

When ignition is turned on, ABS and BRAKE warning lights will illuminate for 2 seconds, then turn off as bulb check. EBCM performs self-check of 4WAL system, once each ignition cycle, when vehicle speed reaches 8 MPH. If faults are detected, ABS indicator light will illuminate (in most cases) and 4WAL functions will be disabled. A related Diagnostic Trouble Code (DTC) will be stored. The BRAKE light illuminates if parking brake is applied or a mechanical brake problem is detected.

When brake pedal is depressed, brake switch voltage to PCM/VCM drops from 12 volts to one volt. At this point, PCM/VCM monitors wheel speed through an AC signal generated by speed sensors located at each wheel. If the deceleration rate of wheel speed reaches a preprogrammed rate, PCM/VCM will activate various control valves to prevent wheel lock-up by increasing or decreasing hydraulic pressure to each channel: left front, right front or rear wheels.