The Powertrain On-Board Diagnostic (OBD) System Check is an organized approach to identifying a problem created by a control module system malfunction. The Powertrain On-Board Diagnostic (OBD) System Check is the starting point for any driveability complaint diagnosis. The Powertrain On-Board Diagnostic (OBD) System Check directs the service technician to the next logical step in diagnosing the complaint.

DO NOT PERFORM THIS CHECK IF NO DRIVEABILITY COMPLAINT EXISTS.

Understanding and using the table correctly will reduce the diagnostic time and prevent the replacement of good parts.

Important: For Domestic and Export DTC Types, refer to DTC Type.

Important: This vehicle is equipped with a Powertrain Control Module (PCM) utilizing an Electrically Erasable Programmable Read Only Memory (EEPROM). When diagnostics call for replacement of the PCM, the PCM must be programmed. Refer to Powertrain Control Module Replacement .

Important: If an intermittent condition exists, check for improper installation of electrical components. Inspect for aftermarket theft deterrent devices, lights, and cellular phones. Ensure that no aftermarket equipment is connected to the Class 2 circuit. If an intermittent condition cannot be located, cellular phone signal communication may be the cause.

The numbers below refer to the step numbers in the diagnostic table.

1. When the ignition is initially turned ON, the MIL will remain ON until the engine is running if no Diagnostic Trouble Codes (DTC's) are stored.

2. This check will determine if any other module(s) on the class 2 circuit can communicate.

3. If multiple DTC's are stored, diagnose in the following order of priority:

1.	PCM/TAC failure DTC's ( P1518, P1517 ).

2.	Component level DTC's (Sensors, Solenoids, Relays etc.). Multiple DTC's within this category should be diagnosed in numerical order starting with the lowest numbered DTC.

3.	System level DTC's (Fuel Trim, etc.).

It is beneficial to review Freeze Frame Data and /or Fail Records. Use the odometer information and the fail counter to determine how frequently and how recently the DTC set. This information and the other operating conditions when the DTC set may help diagnose an intermittent problem. Capturing stored information will preserve data that will be lost when instructed to clear information at the end of a diagnostic table, or if a PCM disconnect or replacement occurs during a diagnostic procedure. The data is stored in the scan tool's memory. The captured information should be reviewed at the end of the diagnostic table to catch the next DTC in the event multiple DTC's were stored. Follow the order of priority as listed above.

4. This step determines if the engine will crank.

5. This step verifies that the engine will start.

6. Comparison of the actual control system data with the Typical Scan Tool Data Values is a quick check to determine if any parameter is not within limits. A base engine problem, such as advanced cam timing, may substantially alter sensor values.