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Home >> GMC >> 2021 >> Yukon AT4 >> Repair and Diagnosis >> Body & Frame >> Towing Systems >> TRAILERING Systems >> Diagnostic Information and Procedures >> Trailer Detection Malfunction (Trailer Brake Detection) >> Circuit/System Verification
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Circuit/System Verification

Verification Procedure If Customer's Trailer Is Available

    NOTE:
    • This test should be used when the customer's trailer (with trailer brakes) is available to use while performing diagnostics.
    • Some trailers require the B+ circuit and the trailer brake control circuit to the X88 Tow Vehicle Electrical Receptacle for trailer brakes to function properly and for the vehicle to detect the trailer is connected on vehicles not equipped with U1D. The vehicle may not show the trailer is connected if either circuit has a fault.
    • A circuit fault or damage with the customer supplied equipment is not diagnosed or supported by GM service information.
  1. Ignition ON/Vehicle in Service Mode.
    2. NOTE:

    Information on identifying the terminals can be found on the cover of the X88 Connector.

  2. Verify a test light illuminates between the trailer B+ terminal at the X88 Tow Vehicle Electrical Receptacle and ground.
    • Go to next step: If the test light illuminates. 
  3. Connect the trailer wiring harness to the X88 Tow Vehicle Electrical Receptacle.
  4. Verify there are no DTCs set.
    • Go to next step: If no DTCs are set 
  5. Verify the vehicle displays a Trailer Connected message on the infotainment screen (P17 Info Display Module).
    • If the vehicle does not display a Trailer Connected message. 
    1. Disconnect the customer's trailer.
    2. Connect the EL-52641  Trailer Presence Simulator Tool. If the EL-52641  Trailer Presence Simulator Tool is not available, connect a simulated trailer, such as a trailer load box tool or a custom trailer simulator with trailer brake diagnostic capabilities. Refer to: Trailering Description and Operation  for more information on creating a simulated trailer tool.
    3. Verify the vehicle displays a Trailer Connected message on the infotainment screen (P17 Info Display Module).
      • Go to next step: If the vehicle does display a Trailer Connected message.
    4. An issue exists with the customer's trailer that is preventing it from being detected by the K133 Trailer Brake Control Module.
    • Go to next step: If the vehicle does display a Trailer Connected message. 
  6. All OK.

Verification Procedure If Customer's Trailer is Unavailable

    NOTE:
    • This test should be used when the customer's trailer (with trailer brakes) is available to use while performing diagnostics.
    • Some trailers require the B+ circuit and the trailer brake control circuit to the X88 Tow Vehicle Electrical Receptacle for trailer brakes to function properly and for the vehicle to detect the trailer is connected on vehicles not equipped with U1D. The vehicle may not show the trailer is connected if either circuit has a fault.
    • A circuit fault or damage with the customer supplied equipment is not diagnosed or supported by GM service information.
  1. Ignition ON/Vehicle in Service Mode.
  2. Verify a test light illuminates between terminal E at the X88 Tow Vehicle Electrical Receptacle and ground.
    • Go to next step: If the test light illuminates. 
  3. Verify there are no DTCs set.
    • Go to next step: If no DTCs are set 
  4. Connect the EL-52641  Trailer Presence Simulator Tool. If the EL-52641  Trailer Presence Simulator Tool is not available, connect a simulated trailer, such as a trailer load box tool or a custom trailer simulator with trailer brake diagnostic capabilities. Refer to: Trailering Description and Operation  for more information on creating a simulated trailer tool.
  5. Verify the vehicle displays the message "Trailer Connected" on the infotainment screen (P17 Info Display Module).
    • Go to next step: If the vehicle does display the message Trailer Connected. 
  6. All OK.
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