Preliminary Diagnosis

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NOTE: A TECH-1 tool is required to perform this procedure.

GENERAL INFORMATION
When servicing the Antilock Brake System (ABS), 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. Using the TECH-1, read all current and history Diagnostic Trouble Codes (DTCs). Be certain to note which DTCs are current malfunctions. DO NOT CLEAR DTCs unless directed to do so. Displaying and Reading Diagnostic Trouble Codes (DTC's)

2. Using the TECH-1, read the DTC HISTORY data. Note the DTCs stored and their frequency of failure. Specifically, note the last failure that occurred and the conditions present when this failure occurred. This "last failure" is what brought the customer in for service, and should be the starting point for diagnosis and repair.
3. Perform a vehicle preliminary diagnosis inspection. Preliminary Diagnosis

4. If no DTC, or mechanical component malfunctions are present, test the modulator for proper operation. Use the TECH-1 to isolate the cause of the problem. If the failure is intermittent and not reproducible, test drive the vehicle while using the automatic snapshot feature of the TECH-1. 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 30 to 50 mph (48 to 80 km/h) while triggering the snapshot mode on any ABS 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. Scan Tool "F" Functions

5. Once all system malfunctions have been corrected, clear the ABS DTCs. Clearing Diagnostic Trouble Codes (DTC's)