Normal Operation

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.

The braking energy provided to the trailer is varied with a Pulse Width Modulated (PWM) signal that switches between 0 volts and battery voltage, the higher the duty cycle the more braking power available. The Trailer Brake Control (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 the manual slider switch fully to the left with a gain of 10, there should be more than 10-12 volts supplied to pin 3 of the 7-pin trailer tow connector. When the trailer is connected to the vehicle the Instrument Panel Cluster (IPC) should show the TRAILER CONNECTED message. If the WIRING FAULT ON TRAILER is only message displayed when the trailer is connected, the fault is with the trailer wiring.

Every 4 seconds (when not braking) the TBC module sends a voltage pulse to pin 3 of the 7-pin trailer tow connector to determine whether or not a trailer is connected.

DTC C2806 (Trailer Brakes Wiring Circuit Short to Vbatt) - this DTC sets in continuous memory when the TBC module detects that the battery voltage is greater than 9 volts while not braking. The TBC module shuts off the trailer brake output and then shuts down.
DTC C2807 (Trailer Brakes Wiring Circuit Short to Ground) - this DTC sets in continuous memory or on-demand when the TBC module detects that the battery voltage drops by more than 20 percent during a braking event or the trailer brakes are drawing more than 28 amps. The TBC module shuts off the trailer brake output and then shuts down.

This pinpoint test is intended to diagnose the following:

Wiring, terminals or connectors
TBC module
Customer trailer