Pinpoint Test C: The Message Center Displays TRAILER FAULT
Auxiliary Brake System - Trailer Brake Control (TBC) Module
Pinpoint Test C: The Message Center Displays TRAILER FAULT
NOTE: Carry out all pinpoint tests without a trailer connected to the vehicle.
Refer to Wiring Diagram Set 95, Trailer/Camper Adapter for schematic and connector information. Diagrams By Number
Normal Operation
The braking energy that is provided to the trailer is varied with a Pulse Width Modulated (PWM) signal along circuit CAT19 (BU) that switches between 0 volt 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 pressure transducer, 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 greater than 10-12 volts supplied to pin 3 of trailer tow connector C439A along circuit CAT19 (BU).
When there is no input to the TBC module from the stoplamp switch or the manual sliding lever, the module sends a voltage pulse along circuit CAT19 (BU) to pin-3 of the 7-pin trailer tow connector every 4 seconds to determine whether or not a trailer is connected.
The factory 7-pin trailer tow connector is attached with a bracket to the rear bumper of the vehicle or to the trailer hitch (if equipped). The 7-pin trailer tow connector acts as a jumper connection between C439A (female) and the trailer electrical connector (female).
- DTC C2806 (Trailer Brakes Wiring Circuit Short to Voltage) - If the voltage on circuit CAT19 (BU) is equal to or greater than 9 volts for 200 ms or more, while not braking, the TBC module sends the TRAILER FAULT message to the Instrument Cluster (IC), shuts off trailer brake output and then shuts down.
- DTC C2807 (Trailer Brakes Wiring Circuit Short to Ground) - If voltage on circuit CAT19 (BU) drops by more than 20% for 200 ms or more during a braking event, or for 1.5 ms or more during an on-demand self test, the TBC module sends the TRAILER FAULT message to the IC, shuts off trailer brake output and then shuts down. This DTC can also be set if the trailer brakes draw more than 28 Amps for 20 ms or more.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- TBC module
- Customer trailer
PINPOINT TEST C: THE MESSAGE CENTER DISPLAYS TRAILER FAULT
NOTICE: 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.
C1-C5:
C5-C7:
C7-C9:
