Diagnostic Aids

Enter this procedure only when DTCs have not been successfully retrieved or if directed here from another test or chart. This symptom test is only intended to diagnose:

• ABS warning light circuit for open or short to ground.
• BRAKE warning indicator light circuit for open or short to ground.
• Malfunction in ABS proportioning system.
• Malfunction in ABS CM.
• ABS CM power (terminal "Z") circuits for low voltage (below 8.5 volts).

1. Check for ABS related DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES  under DIAGNOSIS & TESTING. If an NGS scan tool communication error message exists, repair according to procedures displayed on NGS scan tool. If communication error message still exists after making repairs, go to step  3 . If no ABS related DTCs are present, go to next step. If ABS related DTCs are present, perform appropriate diagnostic test in DIAGNOSTIC TESTS  .
2. Perform PID/DATA MONITOR PROCEDURE  under ADDITIONAL SYSTEM FUNCTIONS. Select PIDs ABSLAMP (ABS warning light), BRKLAMP (BRAKE warning light) and B+ (battery power). Monitor B+ PID, while road testing vehicle under conditions in which warning lights illuminates. If B+ PID value is more than 10 volts when ABSLAMP and/or BRKLAMP PID values reads ON and when ABS and BRAKE warning lights illuminate, replace ABS CM for internal open or short to ground. If B+ PID value is 10 volts or less when ABSLAMP and/or BRKLAMP PID value reads ON and when ABS and BRAKE warning lights illuminate, go to next step.
3. Ensure harness connector and terminals at ABS CM are fully seated and securely connected. Repair connection or replace connector or terminal(s) as necessary, then go to next step. If connection is secure, go to step  5 .
4. Road test vehicle under conditions in which both ABS and BRAKE warning lights illuminate. If both ABS and BRAKE warning lights illuminate again, check ABS CM power supply (terminal "Z") and ground circuit (terminal "AA") for opens and shorts. See WIRING DIAGRAMS  . If neither ABS or BRAKE warning lights illuminate again, a temporary poor contact in wiring may have occurred and ABS is now functioning properly.
5. Ensure ignition switch is turned to OFF position. Check continuity between ABS CM harness connector terminal "T" (Brown/White wire) and DLC-1 terminal No. 2 (Brown/White wire). See Figure and Figure . If continuity exists, go to next step. If continuity does not exist, repair open in Brown/White wire between ABS CM and DLC-1. See WIRING DIAGRAMS  .
6. Turn ignition switch to ON position. Measure voltage between chassis ground and ABS CM harness connector terminal "T" (Brown/White wire). See Figure . If voltage is not present, go to next step. If voltage is present, repair short to battery power in affected wire between ABS CM and DLC-1 terminal No. 2. See WIRING DIAGRAMS  .
7. Turn ignition switch to OFF position. Check continuity between chassis ground and ABS CM harness connector terminal "T" (Brown/White wire). See Figure . If continuity exists, repair short to ground in affected wire between ABS CM and DLC-1 terminal No. 2. See WIRING DIAGRAMS  . If continuity does not exist, check ABS CM power supply (terminal "Z") and ground circuit (terminal "AA") for opens. See WIRING DIAGRAMS  . If ABS CM power supply and ground circuits are okay, replace ABS CM for malfunction in communication circuit.