Pinpoint Test F: The Trailer Brakes Are Inoperative

WARNING: This page is about a different car, the 2006 Ford Pickup, 2006 Ford F550 Super Duty, 2006 Ford F450 Super Duty, and 2006 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.

CAUTION: Use the flex probe kit for all test connections to prevent damage to the wiring terminals. Do not use standard multimeter probes.

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

F1 CHECK FOR ANY ANTI-LOCK BRAKE SYSTEM (ABS) MODULE DIAGNOSTIC TROUBLE CODES (DTCs)
- Key in OFF position.
- Carry out the ABS module self-test. Retrieve and record any ABS module DTCs.
- Are any ABS module DTCs retrieved?
Yes : REFER to VEHICLE DYNAMIC SYSTEMS .

No : GO to F2.
F2 CHECK THE TRAILER BRAKE CONTROL (TBC) MODULE OUTPUT
- Key in ON position.
- Enter the following diagnostic mode on the scan tool: TBC BOO PID.
- Monitor the TBC BOO PID while firmly pressing and releasing the brake pedal.
- Does the TBC BOO PID agree with the stoplamp switch?
Yes : GO to F3.

No : VERIFY brake switch operation. If OK, GO to F4. If not OK, GO to EXTERIOR LIGHTING .
F3 CHECK CIRCUIT 43 (DB) FOR VOLTAGE
NOTE: Battery voltage must be greater than 10 volts.
- Key in OFF position.
- Disconnect: Trailer Tow C4099.
- Key in ON position.
- 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 43 (DB), harness side and ground.
  
  Fig 1: Measuring Voltage Between connector 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 for an overload condition.

No : GO to F4.
F4 CHECK CIRCUIT 43 (DB) FOR AN OPEN
- Key in OFF position.
- Disconnect: TBC Module C2142a.
- Measure the resistance between trailer tow C4099-3, circuit 43 (DB), harness side and TBC C2142a-3, circuit 43 (DB), harness side.
  
  Fig 2: Checking Circuit 43 (DB) For Open
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms?
Yes : The system is operating correctly at this time. The concern may have been caused by the customer's trailer or a loose or corroded connector. TEST the system for normal operation.

No : REPAIR circuit 43 (DB) for an open. TEST the system for normal operation.