Diagnostic Procedure
Important: Understanding the table and using it correctly will reduce diagnosis time and prevent the unnecessary replacement of parts.After the visual inspection is complete, the Diagnostic System Check should be performed. This Powertrain System Check will provide direction for diagnosis of the following:
^ PCM inoperative or damaged, no PCM data or SERVICE ENGINE SOON Malfunction Indicator Lamp (MIL) inoperative.
^ PCM DTCs.
^ Fuel System Rich or Lean.
^ Customer Complaint Driveability Symptoms.
The Diagnostic System Check is designed as a Master table for driveability and emissions system diagnosis. The System Check should always be used as the starting point for all Powertrain diagnosis.
The Diagnostic System Check is an organized approach for identifying a problem. Driver Comments normally fall into one of the following areas:
^ Steady SERVICE ENGINE SOON MIL.
^ Driveability problem
^ Engine will not start or stalls after start.
Diagnostic Procedure Use
The diagnostic procedures used in this section are designed to find and repair powertrain related problems. The general approach is to find the appropriate diagnosis for a problem with five basic steps described below.
1. Understand the customers complaint. It is critical that the technician understand what the customers 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 customers 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 Diagnostic System Check. This is the starting point for the diagnostic procedure, always begin here.
3. Are DTCs displayed? If a DTC is identified by diagnostics, the Diagnostic System Check will direct you to the appropriate table.
4. Is the customers complaint related to a specific powertrain subsystem? If no related DTCs 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.