Preliminary Check

Verify customer complaint by operating suspected system. Visually inspect for obvious signs of mechanical and electrical damage. Check battery voltage. Battery voltage must be at least 10.5 volts. Inspect for system related blown fuses and damaged relays. Inspect for loose or corroded connections, damaged wiring harnesses and/or switches. Check for a broken or partially broken wire inside insulation, which could cause system malfunction but prove good in a continuity/voltage check with system disconnected. Ensure ABS control module harness connector is securely connected and is not corroded or damaged. Ensure any aftermarket electronic equipment is properly installed. If fault is found, repair as necessary. Test drive vehicle. If ANTI-LOCK warning light comes on at low speed, motor relay, solenoid valve or wheel speed sensor malfunction is indicated. Repair or replace as necessary. Check conventional brake system components for proper operation. Check mechanical lock of hydraulic unit solenoid valve. Check for plugged hydraulic line in hydraulic unit. Repair or replace as necessary. Ensure wheel speed sensor rotor gap is correct. See WHEEL SPEED SENSOR  under ADJUSTMENTS. Check for faulty wheel speed sensor. See WHEEL SPEED SENSOR  under COMPONENT TESTING. Replace sensor as necessary. See WHEEL SPEED SENSOR  under REMOVAL & INSTALLATION. If no fault is found, check for ABS related DTCs. See RETRIEVING DTCS  under SELF-DIAGNOSTIC SYSTEM. If no DTCs are displayed, fault may be intermittent. Check for poor connection at ABS ECU. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal connection. Inspect wiring harness for damage. Move connectors and wiring harnesses related to failure. If no diagnostic output exists, check for faulty wiring harness between ABS ECU and data link connector. See WIRING DIAGRAMS  . Repair or replace as necessary.