Refer to Engine Controls Schematics
PCM Power, Grounding, MIL and DLC
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Circuit Description
The Powertrain On-Board Diagnostic (OBD) System Check is an organized approach in identifying a problem created by an electronic engine system fault. The OBD system check is the starting point for any driveability diagnosis. The OBD system check directs the service technician to the next step in diagnosing the complaint. Do not perform this check if no driveability complaint exists. Understanding the table correctly reduces the diagnostic time. Understanding the table correctly prevents the replacement of good parts.
Diagnostic Aids
Important: Do not clear the DTCs unless directed by a diagnostic procedure. Clearing the DTCs will also clear valuable freeze frame and failure records data.
Inspect all related wiring and connections including the connections at the PCM. These may cause an intermittent malfunction.
Check any circuitry that is suspected of causing an intermittent problem for the following conditions:
| • | Backed out terminals |
| • | Improper mating |
| • | Broken locks |
| • | Improperly formed or damaged terminals |
| • | Poor terminal to wiring connections |
| • | Physical damage to the wiring harness |
| • | Corrosion |
Test Description
The numbers below refer to the step number in the diagnostic table.
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This step will check for power and grounds to the data link connector (DLC).
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This step will determine if other modules on the Class 2 circuit can communicate, if no communication occurs, the class 2 circuit is grounded, open, shorted to voltage or the module is causing a communication problem.
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This step will check for DTCs associated with the Vehicle Theft Deterrent (VTD) which will prevent the vehicle from starting.
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Whenever multiple DTCs are stored, refer to the DTCs in the following order:
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Checking the sensors for proper operation during warm up can be a crucial step in correctly diagnosing any driveability concern. Careful observation of these sensors during the engine warm up may reveal a slow responding sensor or a sensor that malfunctions only within a small portion of its range.
After the engine is at the normal operating temperature, a comparison of the actual control system data with the typical values is a quick way 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.
Check the engine coolant temperature (ECT) sensor for initial coolant temperature reading at ambient. Then observe the rise in the temperature while the engine is warming up.
| 1. | PCM Error DTCs |
| 2. | System voltage DTCs |
| 3. | Component level DTCs (DTCs that indicate a malfunctioning part) |
| 4. | System level DTCs (DTCs that indicate a system fault) |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
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Important: Check for applicable service bulletins before proceeding with this diagnosis. Important: Do not turn OFF the ignition when performing this diagnostic.
Does the scan tool power-up? | -- | |||
2 |
Does the scan tool display PCM data? | -- | ||
3 | Does the engine start and continue to run? | -- | ||
Attempt to establish communications with other systems connected to the same serial data line (Passlock/EVO, ATC, ABS controllers). Does scan tool communicate with the other systems? | -- | Go to Body and Accessories | ||
Check for PCM DTCs using the scan tool. Were any last test failed, history, or MIL request DTCs set? | -- | Go to applicable DTC table | ||
Is DTC P0215, P1626 or DTC P1631 stored? | -- | Go to applicable DTC table | ||
Are the displayed values normal or within typical ranges? | -- | Go to Symptoms | Go to Diagnostic Aids and Test Descriptions |
