Pinpoint Test D: When the Ignition Key is Turned to the RUN Position, the TBC Module Display Does Light Up/Prove Out but the Tr

Auxiliary Brake System - Trailer Brake Control (TBC) Module

Pinpoint Test D: When the Ignition Key is Turned to the RUN Position, the TBC Module Display Does Light Up/Prove Out but the Trailer Brakes are Inoperative

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 trailer tow C439A-3 circuit CAT19 (BU).

The TBC module receives Brake Pedal Position (BPP) (stoplamp) switch information from the PCM over the High Speed Controller Area Network (HS-CAN) bus. The TBC module also receives several sensor input messages (brake pressure switch, wheel speed, sensor cluster, ABS system status, etc.) from the ABS module over the HS-CAN bus. If there is a problem in the ABS module that is preventing this information from being sent to the TBC module, the TBC module will enter a limited operating mode. The TBC module receives fused battery voltage from Battery Junction Box (BJB) fuse 17 (30A) along circuit SBB17 (RD) and fused ignition voltage from Smart Junction Box (SJB) fuse 33 (10A) along circuit CBP33 (WH/BN). The ground path for the TBC module is along circuit GD138 (BK/WH).

This pinpoint test is intended to diagnose the following:
- Fuse(s)
- Wiring, terminals or connectors
- ABS module
- TBC module
- Customer trailer



PINPOINT TEST D: WHEN THE IGNITION KEY IS TURNED TO THE RUN POSITION, THE TBC MODULE DISPLAY DOES LIGHT UP/PROVE OUT BUT THE TRAILER BRAKES ARE INOPERATIVE

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.

D1-D5:

D5-D7:

D7-D8: