Test 1A: Checking System For Faults

NOTE: Perform PRE-DIAGNOSTIC INSPECTION before proceeding. To identify circuits, connectors and terminals referenced in testing, see WIRING DIAGRAMS and CONNECTOR IDENTIFICATION . After completing repairs as instructed during specific DTC tests, perform TEST VER-1A to verify problem has been corrected.

Perform a visual inspection of ABS components, wiring harnesses and connectors. Repair obvious problems before continuing. Verify brakelights are operational. Repair brakelights as necessary before continuing.
Connect scan tool to Data Link Connector (DLC). DLC is located under dash, to left of steering column. If scan tool displays NO RESPONSE, perform TEST 19A . If scan tool does not display NO RESPONSE, go to next step.
Read and record all ABS Diagnostic Trouble Codes (DTCs). If CAB power feed circuit DTC is set, perform TEST 11A . CAB power feed circuit DTC must be repaired before diagnosing other DTCs.
If no DTCs are present, select INPUTS/OUTPUTS on scan tool. Read brake switch input as brake pedal is pressed and released. If scan tool display does not match brake pedal position, perform TEST 17A . If scan tool display matches brake pedal position, go to next step.
If a problem exists with Amber ABS warning light or Red BRAKE light, perform appropriate test listed in DIAGNOSTIC TROUBLE CODE DEFINITION table. If no problem exists with warning lights, go to next step.
Read Traction Control Switch (TCS) input as TCS is pressed and released. If scan tool display does not match TCS position, perform TEST 16A . If scan tool display matches TCS position, go to next step.
Disconnect scan tool from DLC. Road test vehicle. Scan tool must be disconnected before road testing vehicle. Perform several ABS stops from more than 30 MPH, then repeat steps 2 , 3 and 4 . If any DTCs are set, perform appropriate test(s).
During test drive, following conditions are normal and no repairs should be attempted to correct these conditions:
- Slight brake pedal drop and a pop noise when ignition is initially turned on.
- When vehicle is first driven off, a humming sound may be heard and/or felt.
- Groaning, popping and/or ticking may be heard inside passenger compartment during an ABS stop.
- Brake pedal feedback (clicking and vibrating) during ABS stop.
- Brake pedal ratcheting down at end of an ABS stop.
If complaint is ABS cycling at end of a stop at low vehicle speeds, it may be caused by a marginal wheel speed sensor signal. Brakes hanging up, sensor air gap or tone wheel condition are possible causes of ABS cycling at end of a stop at low vehicle speeds. After road test, if no problems are found, check if any Technical Service Bulletins (TSBs) apply to vehicle.