Pinpoint Test A : The Trailer Brakes Are Inoperative: Notes

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.

Refer to Trailer/Camper Adapter , for schematic and connector information.

Normal Operation and Fault Conditions

The braking energy provided to the trailer is modulated with a PWM signal which varies between 0 volts and battery voltage, the higher the duty cycle the more braking power available. The TBC module varies the PWM signal based on various inputs such as the brake torque message, the manual slider switch and the gain buttons. With the vehicle stationary and with the manual slider switch fully to the left with a gain of 10, there should be more than 10-12 volts supplied to the trailer tow connector.

The TBC module receives stoplamp switch information directly from the stoplamp switch and from the PCM over the HS-CAN, the TBC module receives additional information from the ABS module over the HS-CAN. If there is a problem in the ABS module preventing this information from being sent to the TBC module, the TBC module enters a limited operating mode. The TBC module receives fused battery voltage from the BJB.

Possible Causes

Fuse
Wiring, terminals or connectors
TBC module
Trailer

Visual Inspection and Diagnostic Pre-checks

Make sure BJB fuse 18 (30A) is OK.
Make sure SJB fuse 31 (5A) is OK.