Pre-Diagnostic Troubleshooting

Perform the Pre-Diagnostic Troubleshooting procedure

Step 1
Before diagnosing the DTC, perform the following checklist :
  • With the scan tool, read all ECU DTC and record on the repair order.
  • Check for DTC in the other modules that may cause a PCM related DTC to set.
  • With the scan tool, run a Vehicle Scan Report and save the file for future use.


  • Check the vehicle repair history for any recent repairs that may be related to the customer complaint.
  • Verify that the battery is fully charged and meets OEM specification.
  • With the scan tool, verify that the battery voltage to the PCM matches the actual battery voltage of the vehicle.
  • With the scan tool, check the PCM for software updates that are related to the DTC or customer complaint. If a flash update is available, read the Service Bulletin to determine if the software update is applicable to the customer complaint before updating the module.
  • Perform any Service Bulletins or other procedures that may apply.
  • Check for aftermarket electrical accessories. Be certain they are installed properly and do not interfere with any related power, ground, or signal circuits. Be certain aftermarket wiring harness are routed away from vehicle wiring harness to avoid electromagnetic interference (EMI) where applicable.
  • If necessary, check the vehicle build configuration and compare with the OEM vehicle Build configuration. Properly configure the vehicle if necessary.

Step 2
If multiple DTC are set in the PCM, and no detectable pattern is evident (i.e. the DTC are not related to just one or two components or subsystems), check the PCM ground circuits for proper continuity. As a general rule, diagnose that DTC in the following order unless instructed to do so by the specific DTC procedure  :
  • ECU Configuration DTC.
  • PCM High or low voltage DTC.
  • PCM Internal error DTC.
  • Communication DTC (see below).
  • 5 Volt sensor reference high or low DTC.
  • Circuit fault DTC (Circuit low, circuit high, open circuit, etc.)
  • Performance / rationality DTC.
  • Other.

Step 3
If multiple communication DTC are set, diagnose the DTC in the following order unless instructed to do so by the specific DTC procedure :
  • CAN Bus off.
  • CAN Bus off performance.
  • Lost Communication.
  • Implausible or invalid data.
  • Missing message.
  • Other.

Were any of the above conditions found ?

Yes, perform the appropriate reapir procedure. Perform the Powertrain Verification Test.
No, perform the diagnostic test procedure related to the DTC. Refer to Sitemap/Labels and perform the appropriate diagnostic procedure.

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