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Pinpoint Test Ad: The Trailer Electric Brakes Are Inoperative/Always Applied

WARNING: This page is about a different car, the 2012 Ford Pickup. 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 damage the connector.
NOTE: Before beginning diagnostics, visually inspect the trailer tow connector mounted on the bumper for signs of corrosion or damage. Repair or install a new trailer tow connector as required.
NOTE: Make sure the vehicle stoplamps operate correctly before beginning diagnostics of the trailer brakes.
  1. AD1 CHECK THE TRAILER ELECTRIC BRAKE CONTROLLER FOR A SHORTED OUTPUT 
    • Ignition ON.
    • Measure the voltage between the trailer tow connector electric brake control supply pin, circuit CAT19 (BU), component side and ground.
      Fig 1: Measuring Voltage Between Trailer Tow Connector Electric Brake Control Supply Pin, Circuit CAT19 (BU), Component Side And Ground
      G06065353Courtesy of FORD MOTOR CO.
    • Is any voltage present? 
      • Yes  : GO to AD2.
      • No  : GO to  AD3.
  2. AD2 CHECK THE TBC MODULE OUTPUT CIRCUIT FOR A SHORT TO VOLTAGE 
    • Disconnect: TBC Module C2142.
    • Measure the voltage between the trailer tow connector electric brake control supply pin, circuit CAT19 (BU), component side and ground.
      Fig 2: Measuring Voltage Between Trailer Tow Connector Electric Brake Control Supply Pin, Circuit CAT19 (BU), Component Side And Ground
      G06065353Courtesy of FORD MOTOR CO.
    • Is any voltage present? 
      • Yes  : REPAIR circuit CAT19 (BU) for a short to voltage. TEST the system for normal operation.
      • No  : INSTALL a new TBC module. TEST the system for normal operation.
  3. AD3 CHECK THE TBC MODULE OUTPUT 
    • Set the gain on the trailer electric brake controller to the maximum setting.
    • While applying the brake pedal, measure the voltage between the trailer tow connector electric brake control supply pin, circuit CAT19 (BU), component side and ground.
      Fig 3: Measuring Voltage Between Trailer Tow Connector Electric Brake Control Supply Pin, Circuit CAT19 (BU), Component Side And Ground
      G06065353Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
      • Yes  : The vehicle is operating correctly. SEND the trailer to an authorized camper/trailer repair facility.
      • No  : GO to AD4.
  4. AD4 CHECK FOR VOLTAGE TO THE TRAILER TOW CONNECTOR (VEHICLE HARNESS) 
    • Disconnect: Trailer Tow C439A.
      • NOTE: Make sure the gain is set to the maximum setting.
      Fig 4: Measuring Voltage Between Trailer Tow C439A-3, Circuit CAT19 (BU), Harness Side And Ground
      G06065356Courtesy of FORD MOTOR CO.
    • While applying the brake pedal, measure the voltage between the trailer tow C439A-3, circuit CAT19 (BU), harness side and ground.
    • Is the voltage greater than 10 volts? 
      • Yes  : INSTALL a new trailer tow connector. TEST the system for normal operation.
      • No  : GO to AD5.
  5. AD5 CHECK FOR VOLTAGE TO THE TBC MODULE 
    • Disconnect: TBC Module C2142.
    • Measure the voltage between the TBC module C2142-8, circuit SBB17 (RD), harness side and ground.
      Fig 5: Measuring Voltage Between TBC Module C2142-8, Circuit SBB17 (RD), Harness Side And Ground
      G06141908Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
      • Yes  : GO to AD6.
      • No  : VERIFY the BJB fuse 17 (30A) is OK. If OK, REPAIR circuit SBB17 (RD) for an open. TEST the system for normal operation. If not OK, REFER to the Wiring Diagrams information to identify the possible causes of the circuit short.
  6. AD6 CHECK THE TBC MODULE GROUND CIRCUIT FOR AN OPEN 
    • Measure the voltage between the trailer electric brake controller C2142-8, circuit SBB17 (RD), harness side and the trailer electric brake controller C2142-3, circuit GD138 (BK/WH), harness side.
      Fig 6: Checking TBC Module Ground Circuit For Open
      G06172752Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
      • Yes  : GO to AD7.
      • No  : REPAIR circuit GD138 (BK/WH) for an open. TEST the system for normal operation.
  7. AD7 CHECK THE STOPLAMP SWITCH INPUT TO THE TBC MODULE 
    • While applying the brake pedal, measure the voltage between the TBC module C2142-12, circuit CBP31 (BU/OG), harness side and ground.
      Fig 7: Measuring Voltage Between TBC Module C2142-12, Circuit CBP31 (BU/OG), Harness Side And Ground
      G06172753Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
      • Yes  : GO to  AD9.
      • No  : VERIFY the BCM fuse 31 (5A) Is OK. If OK, GO to AD8. If not OK, refer to the Wiring Diagrams information to identify the possible causes of the circuit short.
  8. AD8 CHECK THE STOPLAMP SWITCH INPUT CIRCUIT TO THE TBC MODULE FOR AN OPEN 
    • Disconnect: BCM C2280B.
    • Measure the resistance between the TBC module C2142-12, circuit CBP31 (BU/OG), harness side and the BCM C2280B-4, circuit CBP31 (BU/OG), harness side.
      Fig 8: Checking Stoplamp Switch Input Circuit To TBC Module For Open
      G07409923Courtesy of FORD MOTOR CO.
    • Is the resistance less than 5 ohms? 
      • Yes  : GO to  AD11.
      • No  : REPAIR circuit CBP31 (BU/OG) for an open. TEST the system for normal operation.
  9. AD9 CHECK THE TBC MODULE OUTPUT CIRCUIT FOR A SHORT TO GROUND 
    • Measure the resistance between the trailer electric brake controller C2142-14, circuit CAT19 (BU), harness side and ground.
      Fig 9: Measuring Resistance Between Trailer Electric Brake Controller C2142-14, Circuit CAT19 (BU), Harness Side And Ground
      G06141911Courtesy of FORD MOTOR CO.
    • Is the resistance greater than 10, 000 ohms? 
      • Yes  : GO to AD10.
      • No  : REPAIR circuit CAT19 (BU) for a short to ground. TEST the system for normal operation.
  10. AD10 CHECK THE TBC MODULE OUTPUT CIRCUIT FOR AN OPEN 
    • Connect a fused jumper wire between the trailer electric brake controller C2142-8, circuit SBB17 (RD), harness side and the trailer electric brake controller C2142-14, circuit CAT19 (BU), harness side.
      Fig 10: Connecting Fused Jumper Wire Between Trailer Electric Brake Controller C2142-8, Circuit SBB17 (RD) And C2142-14, Circuit CAT19 (BU)
      G06141912Courtesy of FORD MOTOR CO.
    • Measure the voltage between the trailer tow C439A-3, circuit CAT19 (BU), harness side and ground.
      Fig 11: Measuring Voltage Between Trailer Tow C439A-3, Circuit CAT19 (BU), Harness Side And Ground
      G06065356Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
      • Yes  : INSTALL a new trailer electric brake controller. TEST the system for normal operation.
      • No  : REPAIR circuit CAT19 (BU) for an open. TEST the system for normal operation.
  11. AD11 CHECK FOR CORRECT BCM OPERATION 
    • Disconnect all the BCM connectors.
    • Check for:
      • corrosion
      • damaged pins
      • pushed-out pins
    • Connect all the BCM connectors and make sure they seat correctly.
    • Operate the system and verify the concern is still present.
    • Is the concern still present? 
      • Yes  : INSTALL a new BCM. REFER to MULTIFUNCTION ELECTRONIC MODULES . TEST the system for normal operation.
      • No  : The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector.
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