- Flow of Diagnosis - Start Here

Powertrain Diagnosis:

DIAGNOSTIC PROCEDURE USE
The diagnostic procedures are designed to find and repair powertrain related problems. The general approach is to find the appropriate diagnosis for a problem with six basic steps shown in the accompanying image and described below.

1. Understand the customer's complaint. It is critical that the technician understand what the customer's complaint is. Failure to understand this may lead to misdiagnosis or unnecessary diagnosis. Among other things, the technician must know whether the condition is present at all times, only under certain circumstances, or truly intermittent (random). This will assist the technician in duplicating and diagnosing the problem. Another reason the technician must understand the customer's complaint is so the technician may determine whether the complaint requires service or is normal vehicle operation. Trying to diagnose a complaint that is normal will waste time and may result in unnecessary service.

2. Are Diagnostics working properly? Use the Self-Diagnostic System Check. This is the starting point for the diagnostic procedure, always begin here. Testing and Inspection

If the Diagnostics are not working properly, the Powertrain System Check will lead you to a chart under Computers and Control Systems / System Diagnosis / Procedures / Diagnosis by Symptom to correct this condition. Testing and Inspection

3. Are Trouble Codes displayed? If a trouble code is identified by diagnostics, the Powertrain System Check will direct you to the appropriate chart. Refer to Computers and Control Systems / System Diagnosis / Procedures / Vehicle On-Board Diagnostics for the correct procedure to display trouble codes. Testing and Inspection

4. Is the customer's complaint related to a specific powertrain subsystem? If no related trouble codes are set, the next quickest way to locate the problem is to narrow it down to a specific powertrain subsystem. If a specific subsystem can be pinpointed as the cause, it is easier to diagnose.

5. Is the problem powertrain related? Some customer complaints may appear to be powertrain related but are actually caused by other vehicle systems.

6. Select the symptom, listed under Computers and Control Systems / System Diagnosis / Procedures / Diagnosis by Symptom, with the description that best fits the customer complaint. Then begin performing the tests suggested and proceed until the root cause is found. Testing and Inspection