Diagnostic System Check

Description

Important: Do not perform this diagnostic if no driveability concern exists. A driveability condition includes all PCM controlled systems and components.

The Powertrain OBD System Check is an organized approach to identifying a concern created by an electronic engine 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 concern. Understanding and using the table correctly will reduce the diagnostic time and prevent the replacement of good parts.

Important: The DTCs associated with the automatic transmission are:
^ DTCs P0502 and P0503.
^ Any 700 (except P0704, P0705 and P0706) and 1800 series DTCs (i.e. DTC P07XX and P18XX).

Important:
^ When the Body Control Module (BCM) is replaced, the PCM password Learn procedure must be performed. Refer to DTC P1631 Theft Deterrent Password Incorrect for the learn procedure.
^ 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:
- The PCM must be programmed.
- The PCM Password learn procedure must be performed. Refer to DTC P1631 Theft Deterrent Password Incorrect for procedure.
- The Idle Learn Procedure.

Diagnostic Aids
This vehicle has a column lock system. This system is necessary because of the location of the ignition lock cylinder. The BCM controls a motor mounted on the steering column. The purpose of the motor is to unlock the steering wheel. The PCM will disable the fuel if the BCM is unable to determine if either the column is unlocked or vehicle speed is present.

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. If multiple DTCs are set, inspect the IGN relay for proper operation.

Test Description
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.
3. This step determines if any other modules on the Class 2 circuit can communicate. If the scan tool displays Waiting for Data, the class 2 circuit is shorted to ground.
4. An ignition 1 voltage that is low may cause the following conditions:
^ A no start
^ Stalling
^ High engine idle
^ No scan tool communications
6. This step tests for DTCs associated with the Vehicle Theft Deterrent system which prevents the engine from starting.
7. This condition may indicate a concern with the Column Lock system.
8. If multiple DTCs are stored, diagnose in the following order of priority:
1. PCM/TAC failure DTCs (P0601, P0602, P0604, P0606, P1517, P1518)
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.) 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 condition. 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 the 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 concern (i.e. advanced cam timing) may substantially alter sensor values. If the actual data does not correspond with the values in the Engine Scan Tool Data List, refer to the appropriate system/component Diagnostic Aids or Test Description.