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Home >> GMC >> 2024 >> Sierra EV >> Repair and Diagnosis >> Body & Frame >> Towing Systems >> TRAILERING Systems >> Diagnostic Information and Procedures >> DTC B1B55 >> Circuit/System Testing

Circuit/System Testing

    NOTE:
    • This procedure will only diagnose factory installed equipment and wiring up to the X88B Tow Vehicle Electrical Receptacle.
    • A circuit fault or damage with the customer supplied equipment is not diagnosed or supported by GM service information.
  1. Inspect the X88B Tow Vehicle Electrical Receptacle for corrosion and/or visible damage.
    • If corrosion and/or visible damage exists 

      Repair or replace as necessary

    • Go to next step: If no condition exists. 
  2. Ignition/vehicle OFF, disconnect the harness connector at the X88B Tow Vehicle Electrical Receptacle.
  3. Verify a test lamp illuminates between ground circuit terminal B and B+.
    • If the test lamp does not illuminate. 
    1. Repair the open/high resistance on the ground circuit or ground connection.
    • Go to next step: If the test lamp illuminates. 
  4. Connect a test lamp between control circuit terminal F and ground. ignition ON/vehicle in service mode.
  5. Verify the test lamp turns ON and OFF when commanding the Trailer Tail Lamps ON and OFF with a scan tool.
    • If the test lamp is always OFF 
    1. Test circuit 2109 for a short to ground.
      • If a short to ground is found, repair the fault on the circuit.
      • Go to next step: If a short to ground is not found
    2. Test circuit 2109 for an open/high resistance
      • If an open/high resistance is found, repair the fault on the circuit.
      • Go to next step: If an open/high resistance is not found.
    3. Replace the K68 Trailer Lamp Control Module.
    • If the test lamp is always ON 
    1. Test circuit 2109 for a short to voltage.
      • If a short to voltage is found, repair the fault on the circuit.
      • Go to next step: If a short to voltage is not found.
    2. Replace the K68 Trailer Lamp Control Module.
    • Go to next step: If the test lamp turns ON and OFF 
    6. NOTE:

    The control circuit has tested good to this point. Verify the electrical system on the customers trailer is functioning properly before continuing.

  6. Test or replace the X88B Tow Vehicle Electrical Receptacle.
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