Pinpoint Test A: The Trailer Brakes Are Inoperative

WARNING: This page is about a different car, the 2013 Ford F-550 Super Duty, 2013 Ford F-450 Super Duty, 2013 Ford F-350 Super Duty, and 2013 Ford F-250 Super Duty. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Use the Flex Probe Kit for all test connections to prevent damage to the wiring terminals. Do not use standard multi-meter probes.

NOTE: Make sure the trailer brakes are electric-magnet actuated drum type brakes before proceeding with this pinpoint test.

A1 CHECK FOR ANY ABS MODULE OR PCM DTCs
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: ABS Module Self-Test.
- Enter the following diagnostic mode on the scan tool: PCM Self-Test.
- Retrieve and record any ABS module or PCM DTCs.
- Are any ABS module or PCM DTCs retrieved?
- Yes : For ABS DTCs, REFER to ANTI-LOCK BRAKE SYSTEM (ABS) & STABILITY CONTROL .
  For PCM DTCs, REFER to ELECTRONIC ENGINE CONTROLS - GASOLINE ENGINES (gas engine) or ELECTRONIC ENGINE CONTROLS - DIESEL ENGINES (diesel engine).
- No : GO to A2.
A2 CHECK FOR TBC MODULE DTCs
- Review the DTCs retrieved and recorded during TBC module self-test.
- Are any TBC module DTCs present?
- Yes : GO to the Trailer Brake Control (TBC) Module DTC Chart .
- No : GO to A3.
A3 CHECK THE TBC MODULE OUTPUT
NOTE: Battery voltage must be greater than 10 volts.
- Ignition ON.
- NOTE: If the manual slider switch is held to the full left position for more than 5 minutes, the TBC module automatically shuts down.
  
  Have an assistant press the manual slider switch fully to the left with a gain of 10 on the TBC module.
- Measure the voltage between trailer tow C4099-3, circuit CAT19 (BU), harness side and ground.
  
  Fig 1: Measuring Voltage Between Trailer Tow C4099-3, Circuit CAT19 (BU) And Ground
  Courtesy of FORD MOTOR CO.
- Is the voltage greater than 10-12 volts?
- Yes : The TBC module is operating correctly. SEND the trailer to an authorized camper/trailer repair center.
- No : GO to A4.
A4 CHECK THE TBC MODULE PWM OUTPUT CIRCUIT FOR AN OPEN
- Ignition OFF.
- Disconnect: Trailer Tow C4099.
- Disconnect: TBC Module C2142.
- Measure the resistance between trailer tow C4099-3, circuit CAT19 (BU), harness side and TBC module C2142-14, circuit CAT19 (BU), harness side.
  
  Fig 2: Measuring Resistance Between Trailer Tow C4099-3, Circuit CAT19 (BU) And TBC Module C2142-14, Circuit CAT19 (BU)
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms?
- Yes : GO to A5.
- No : REPAIR circuit CAT19 (BU) for an open circuit. TEST the system for normal operation.
A5 CHECK FOR CORRECT TBC MODULE OPERATION
- Disconnect the TBC module connector.
- Check for:
  - corrosion
  - damaged pins
  - pushed-out pins
- Connect the TBC module connector and make sure that it seats correctly.
- Operate the system and verify the concern is still present.
- Is the concern still present?
- Yes : INSTALL a new TBC module. REFER to TRAILER BRAKE CONTROL (TBC) MODULE . 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.