Pre-Diagnostic Troubleshooting Procedure

For a complete wiring diagram, refer to appropriate SYSTEM WIRING DIAGRAMS article  .

The Pre-Diagnostic Troubleshooting Procedure provides a common list of possible causes and must be performed before performing any DTC diagnostic procedure.

After completing any repairs, perform the appropriate VERIFICATION TEST.

1. With the scan tool, read DTCs and record on the repair order  .
2. With the scan tool, create a Vehicle Scan Report and ECU Configuration Report  . Save the files for future use or if additional assistance is needed.
3. Check the vehicle repair history  for any recent repairs that may be related to the customer complaint.
4. If related to the customer complaint, verify the vehicle build configuration  with the OEM Vehicle Build Configuration on DealerCONNECT, TechCONNECT, or Service Library. Properly configure the vehicle, if necessary.
5. If related to the customer complaint, verify all Electronic Control Units (ECU) s have the same Original Vehicle Identification Number (VIN)  . A VIN mismatch can indicate the source of the problem, and could also cause multiple communication DTCs to set.
6. With the scan tool, check all ECUs for available software updates  that may be related to the customer complaint.
   • Review all Service Bulletins to determine if the software update is applicable to the customer complaint.
     • Update the ECU(s), as needed.
     • If the HVAC Module is updated or replaced, perform the HVAC VERIFICATION TEST. Refer to HVAC VERIFICATION TEST .
7. Using the Search function in TechCONNECT or Service Library, check for review any related information under SERVICE ACTIONS/TIPS  .
   • Perform any Service Bulletins or other procedures that may apply.
   • NOTE:  When using Service Library  , refer to the Service Bulletin Recalls  section in the Vehicle Dashboard. Star Online cases can also be located there.
8. Check for aftermarket electrical accessories  , checking for proper installation and that any related power, ground, signal, or communication circuits have been compromised. Also, make sure any wiring harnesses are routed away from vehicle wiring harness to avoid electromagnetic interference (EMI), if applicable.
   NOTE:

   A low battery State Of Charge (SOC), or a charging system that is not operating properly, can cause multiple symptoms or DTCs to set.

9. If related to the customer complaint, check the vehicle charging system and battery for proper operation  . Refer to the appropriate Service Information.
10. Check other ECUs for DTCs  that may also cause this DTC to set.
11. If multiple DTCs are set in one ECU, and no detectable pattern is evident (i.e. the DTCs are not related to just one or two components or subsystems), check the applicable ECU ground circuit(s) for proper continuity  . As a general rule, diagnose the DTCs in the following order  , unless instructed otherwise by a specific DTC procedure:
    • ECU Configuration DTCs
    • ECU Voltage DTCs
    • ECU Internal Error DTCs
    • Circuit Fault DTCs (Low voltage, High Voltage, Open Circuit, Short Circuit, Low Current, High Current)
    • Communication DTCs (See below)
    • Performance / Rationality DTCs
    • Implausible or Invalid Data
    • Missing Message
    • Other
12. If multiple communication DTCs are set, diagnose the DTCs in the following order  , unless instructed otherwise by a specific DTC procedure:
    1. CAN Bus Off
    2. CAN Bus Off Performance
    3. Lost Communication
    4. Other
    NOTE:

    IMPORTANT: Some Control Modules simply pass information from one Control Module to the other. In some cases, a U-code DTC may be set that implicates the "pass-through" module that sent the information. For example, if an Engine Coolant Temperature (ECT) Sensor DTC is set in the Powertrain Control Module (PCM), the HVAC module may set an "Implausible Data from BCM" DTC because the BCM is the module that normally passes that information from the PCM to the HVAC module. However, the BCM may not set any DTCs related to the faulted ECT Sensor because the BCM does not use the ECT information. In this case, the PCM ECT DTC should be diagnosed before the Implausible Data DTC. If you suspect a scenario like this, diagnose the non U-code DTC(s) before diagnosing any Implausible Data, Implausible Signal, Invalid Data, or Missing Message DTCs.