Diagnostic Process

When servicing the Antilock Brake System/Traction Control System (ABS/TCS), the following steps should be followed in order. Failure to follow these steps may result in the loss of important diagnostic data and may lead to difficult and time-consuming diagnosis procedures:

1. Perform a vehicle preliminary diagnosis inspection. This should include:
- Inspection of the brake master cylinder fluid reservoir for proper brake fluid level and signs of contamination.
- Inspection of the brake modulator for any leaks or wiring damage.
- Inspection of brake components at all four wheels. Verify no drag exists. Also, verify proper brake apply operation.
- Inspection for worn or damaged wheel bearings that may allow a wheel to "wobble."
- Inspection of the wheel speed sensors and their wiring. Verify solid sensor attachment, and undamaged wiring, especially at vehicle attachment points.
- Verify proper outer CV joint alignment and operation.
- Verify tires meet legal tread depth requirements.
2. Perform DIAGNOSTIC SYSTEM CHECK. If any Diagnostic Trouble Codes (DTCs) are displayed, select DTC HISTORY to note the last malfunction that occurred. Diagnose and repair this malfunction first.
3. If no DTCs are present, or mechanical component malfunctions are present, or if the failure is intermittent and not reproducible, test drive the vehicle while using the automatic snapshot feature of the Scan Tool. Perform normal acceleration, stopping, and turning maneuvers. If this does not reproduce the malfunction, perform an ABS stop, on a low coefficient surface such as gravel, from approximately 48-80 km/h (30-50 mph) while triggering the snapshot mode on any ABS/TCS DTC. If the failure is still not reproducible, use the enhanced diagnostic information found in DTC HISTORY to determine whether or not this malfunction should be diagnosed further based on frequency of failure.
4. Once all system malfunctions have been corrected, clear the ABS/TCS DTCs.