Important: Do not perform this check if no driveability concern exists.

The Powertrain On Board Diagnostic (OBD) System Check is an organized approach to identifying a problem created by an electronic powertrain control system malfunction. The Powertrain OBD System Check is the starting point for any driveability concern diagnosis. The Powertrain OBD System Check directs the service technician to the next logical step in diagnosing a driveability concern. Understanding and using the table correctly will reduce the diagnostic time and prevent the replacement of good parts.

Important: For automatic transmission DTCs, refer to Diagnostic Trouble Code (DTC) List/Type in Transmission (4L60E) for diagnosis procedures. The DTCs associated with the automatic transmission are:

Important: For Domestic and Export DTC Types, refer to Diagnostic Trouble Code (DTC) List/Type .

Important: When the body control module (BCM) is replaced the PCM Password Learn procedure must be performed. Refer to DTC P1631 Theft Deterrent Start Enable Signal Not Correct . DTC P1631 sets if the password learn procedure is not performed.

Important: This vehicle is equipped with a powertrain control module (PCM) utilizing an electrically erasable programmable read only memory (EEPROM). Program the new PCM when diagnostics call for replacement of the PCM. When the PCM is replaced, the following must be performed:

1. The PCM must be programed -- Refer to Powertrain Control Module Replacement .
2. The PCM Password Learn procedure -- Refer to DTC P1631 Theft Deterrent Start Enable Signal Not Correct for details on procedure.
3. The CKP System Variation Learn procedure -- Refer to Crankshaft Position System Variation Learn .
4. The Idle Learn procedure -- Refer to Idle Learn .
5. When the PCMs power is interrupted or is reprogrammed, the Idle Learn procedure must be performed. Refer to Idle Learn .

Important: If an intermittent condition exists, inspect the PCM wiring harnesses 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. A cellular phone signal communication may cause an intermittent condition.

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

1. Use a properly functioning scan tool with the diagnostic tables in this section. DO NOT use the Clear Info function unless instructed by a diagnostic procedure.

2. This step checks that the scan tool communicates with the PCM.

3. This step checks that the scan tool communicates with all other modules on the Class 2 Circuit.

4. An ignition 1 voltage that is too low may cause the following conditions:

•	A no start

•

Stalling

•

High idle

•	An inoperative scan tool

6. This step checks for DTCs associated with the Vehicle Theft Deterrent (VTD) system which will prevent the engine from starting. A problem with the BCM causes this condition. If the BCM is not powered up, the PCM does not receive a password and the engine starts and stalls.

7. If the VCM/PCM Fuel Continue parameter displays NO, this indicates the BCM is not sending the PCM the password.

8. If multiple DTCs are stored, diagnose in the following order of priority:

1.	PCM failure DTCs (P0601, P0602, P0604)

2.	System Voltage DTCs

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

4.	System level DTCs (Misfire, Fuel Trim, etc.)

For Automatic Transmission DTCs, Refer to Diagnostic Trouble Code (DTC) List/Type (4L60-E) or Diagnostic Trouble Code (DTC) List/Type (4L80-E) in Automatic Transmission.

It is beneficial to review the Freeze Frame Data and/or Fail Records. Use the odometer information and the fail counter in order 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 the stored info preserves data that the PCM will lose when instructed to Clear Info at the end of a diagnostic table, or if you disconnect the PCM or replace the PCM during a diagnostic procedure. The scan tool stores the data in the scan tool's memory. Review the captured info at the end of the diagnostic procedure in order to catch the next DTC in the event there are multiple DTCs stored. Follow the order of priority as listed above.

9. Compare actual control system data with the values in the Engine Scan Tool Data List to determine if any parameter is not within limits. Keep in mind that a base engine problem (i.e. advanced cam timing) may substantially alter sensor values. If the actual data does not correspond with the values in the Scan Tool Data List , refer to the appropriate system/component diagnostic aids or test descriptions.