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Pinpoint Test B : The Trailer Brakes Are Always Engaged

WARNING: This page is about a different car, the 2016 Ford Expedition. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may cause damage to the connector.

  1. B1 CHECK FOR ANY TBC MODULE OR PCM DTCs

    • Ignition ON.
    • Using a diagnostic scan tool, carry out the TBC module self-test.
    • Using a diagnostic scan tool, carry out the PCM KOEO self-test.
    • Retrieve and record any TBC module or PCM DTCs.

    Are any DTCs present in the TBC module or the PCM? 

    Yes  For TBC module DTCs, GO to the DTC Chart: TBC Module .For PCM DTCs, REFER to Diagnosis and Testing in Electronic Engine Controls .
    No  GO to  B2.

  2. B2 OBSERVE THE VEHICLE STOPLAMP OPERATION

    • Monitor the vehicle stoplamps while pressing and releasing the brake pedal.

    Do the vehicle stoplamps operate correctly? 

    Yes  GO to  B3.
    No  REFER to Diagnosis and Testing in Exterior Lighting to diagnose the stoplamp switch.

  3. B3 CHECK THE TBC MODULE OUTPUT

    NOTE: Every 4 seconds a voltage pulse is applied to the circuit as a diagnostic test.

    • Ignition OFF.
    • Disconnect trailer tow C4099 .
    • Ignition ON.
    • Make sure the brake pedal is not  pressed and the manual slider switch is not  being applied.
    • Measure:
      Positive Lead Measurement / Action Negative Lead
      C4099-3
      GFD134422Courtesy of FORD MOTOR COMPANY
      		 Ground

    Is steady voltage indicated? 

    Yes  GO to  B4.
    No  The TBC module and vehicle wiring are operating correctly. SEND the trailer to an authorized camper/trailer repair facility.

  4. B4 CHECK THE TBC MODULE PWM OUTPUT CIRCUIT FOR A SHORT TO VOLTAGE

    • Ignition OFF.
    • Disconnect TBC module C2142 .
    • Ignition ON.
    • Measure:
      Positive Lead Measurement / Action Negative Lead
      C4099-3
      GFD134422Courtesy of FORD MOTOR COMPANY
      		 Ground

    Is any voltage present? 

    Yes  REPAIR the circuit.
    No  GO to  B5.

  5. B5 CHECK FOR CORRECT TBC MODULE OPERATION

    • Disconnect and inspect TBC module C2142 .
    • Repair:
      • corrosion (install new connector or terminal - clean module pins)
      • damaged or bent pins - install new terminals or pins
      • pushed-out pins - install new pins as necessary
    • Connect TBC module C2142 , make sure it seats and latches correctly.
    • Connect trailer tow C4099 , make sure it seats and latches correctly.
    • Operate the system and verify the concern is still present.

    Is the concern still present? 

    Yes  CHECK OASIS for any applicable TSBs. If a TSB exists for this concern, DISCONTINUE this test and FOLLOW the TSB instructions. If no TSBs address this concern, INSTALL a new TBC module. REFER to Trailer Brake Control (TBC) Module .
    No  The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. ADDRESS the root cause of any connector or pin issues.
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