Diagnostic Notes (Checking the Basics)

NOTE: This section is used to find the correct test procedure for a given symptom. The symptoms and actions in this section are EMISSION RELATED ONLY. Verify the correct system application to ensure that the vehicle has the given component.

NOTE: For catalytic converter and feedback system to function properly, it is essential that vehicle is at operating temperature, (except when attempting to diagnose cold start or cold driveability problem).

TIP: Use the FLOW OF DIAGNOSIS as a path for systematic diagnosis.

ALL DIAGNOSIS SHOULD FOLLOW THESE STEPS
1) VERIFY CUSTOMER COMPLAINT
The first step in systematic diagnosis is to understand the customer's complaint and verify that it is not normal operation.

- Use the Vehicle Repair History And Driveability Worksheets In TECHNICAL/ MANAGEMENT SUPPORT to provide better communication between the customer and the mechanic.

- The vehicle repair history can provide explanations to unusual complaints which seem to elude normal troubleshooting attempts. Incorrect components or unapproved repairs can have subtle influences on seemingly unrelated systems.

- Check any Technical Service Bulletins that may apply to the vehicle being serviced.

2) EXTRACT TROUBLE CODES
Extracting trouble codes identifies any obvious problem areas and verifies operation of the on board diagnostic system.

- Diagnostic Trouble Codes are cleared whenever the Engine Controller or the battery is disconnected. Therefore, all fault codes should be read prior to any vehicle power interruption or troubleshooting.

- Diagnose and repair any fault code related problems before proceeding with further diagnosis.

3) PERFORM VISUAL INSPECTION:
A thorough visual inspection can save hours of diagnostic time.

- Many electrical problems can be seen with the naked eye, i.e. burned or melted insulation, blackened components etc..

4) CHECK FOR RELATED SYMPTOMS AND ISOLATE PROBLEM
Test components and systems to isolate cause of problem.

Avoid correcting symptoms without fixing the problem(s) causing the symptoms.

5) REPAIR PROBLEM
Perform needed repairs.

6) VERIFY PROPER OPERATION
Verify that repairs have fixed the complaint by performing verification test when possible.

If there is no verification test for the procedure used, attempt to operate the repaired system.