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 concern. Do not perform this check if no driveability concern 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 numbers in the diagnostic table.
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This step determines if the scan tool powers up when connected to the DLC.
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The MIL should be ON when the ignition is turned ON.
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Refer to DTC List (DTC Type Table Domestic) for a list of valid DTCs.
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Refer to Data Link Connector (DLC) Schematics in Data Link Communications to determine all of the modules communicating on the Class 2 Serial Data circuit. If any of the modules are not present in the Diagnostic Circuit Check, then the modules never established communications. The scan tool will indicate a YES state for communicating modules and a NO state for modules that had established, yet no longer communicate.
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If the vehicle does not start or starts and stalls, the Passlock System could be the cause.
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This test determines if the MIL can be controlled by the VCM.
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Comparing the ACTUAL and TYPICAL scan tool data values will aid in determining whether an engine parameter is within limits (i.e., advanced timing can substantially alter sensor values.)
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Important:
Does the scan tool power-up? | -- | |||||||||||
Turn ON the ignition, with the engine OFF. Is the MIL ON? | -- | Go to Step 3 | ||||||||||
3 | Attempt to establish communications with the PCM. Does the scan tool communicate with the PCM? | -- | Go to Step 4 | |||||||||
Save the DTC Freeze Frame and the Failure Records if any of the following DTC status are set in the scan tool DTC information:
Did you find any DTCs? | -- | Go to applicable DTC table | Go to Step 5 | |||||||||
Monitor the Serial Data Class 2 messages with the scan tool. Are all other modules communicating with the scan tool? | -- | Go to Step 6 | ||||||||||
6 | Attempt to start the engine. Does the engine start and continue to Run? | -- | Go to Step 8 | Go to Step 7 | ||||||||
Check for any passlock DTCs in Body or Chassis. Did you find any DTCs? | -- | Go to applicable DTC table | ||||||||||
Command the MIL OFF with the scan tool. Does the MIL turn OFF? | -- | Go to Step 9 | ||||||||||
Compare the scan tool engine data with the TYPICAL scan tool values. Are the values within the typical ranges? | -- | Go to Symptoms | Go to Diagnostic Aids |
