Pinpoint Test A: The Trailer Brakes are Inoperative

Auxiliary Brake System - Trailer Brake Control (TBC) Module

Pinpoint Test A: The Trailer Brakes are Inoperative



Normal Operation

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 (Pulse Width Modulated) 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 (Trailer Brake Control) module receives stoplamp switch information from the PCM and information from the ABS module over the High Speed Controller Area Network (HS-CAN) bus. If there is a problem in the ABS module that is preventing this information from being sent to the TBC (Trailer Brake Control) module, the TBC (Trailer Brake Control) module enters a limited operating mode. The TBC (Trailer Brake Control) module receives fused battery voltage from Battery Junction Box (BJB) fuse 22 (30A) and fused ignition voltage from Body Control Module (BCM) fuse 35 (5A).

This pinpoint test is intended to diagnose the following:

- Fuse

- Wiring, terminals or connectors

- TBC (Trailer Brake Control) module

- Trailer

PINPOINT TEST A : 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.

A1 CHECK FOR ANY ABS MODULE OR PCM DTCs

- Ignition ON.

- Enter the following diagnostic mode on the scan tool: ABS Module Self-Test.

- Enter the following diagnostic mode on the scan tool: PCM Self-Test.

- Retrieve and record any ABS module or PCM DTCs.

Are any ABS module or PCM DTCs retrieved?

Yes
For ABS DTCs, REFER to Antilock Brakes / Traction Control Systems.

For PCM DTCs, REFER to Computers and Control Systems (gas engine) or Computers and Control Systems (diesel engine).

No
GO to A2.

A2 CHECK FOR TBC (Trailer Brake Control) MODULE DTCs

- Review the DTCs retrieved and recorded during TBC (Trailer Brake Control) module self-test.

Are any TBC (Trailer Brake Control) module DTCs present?

Yes
GO to the Trailer Brake Control (TBC) Module DTC Chart. Trailer Brake Control Module
No
GO to A3.

A3 CHECK THE TBC (Trailer Brake Control) MODULE OUTPUT

NOTE: Battery voltage must be greater than 10 volts.

- Ignition ON.

- NOTE: If the manual slider switch is held to the full left position for more than 5 minutes, the TBC (Trailer Brake Control) module automatically shuts down.
Have an assistant press the manual slider switch fully to the left with a gain of 10 on the TBC (Trailer Brake Control) module.

- Measure the voltage between trailer tow C4099-3, circuit CAT19 (BU), harness side and ground.





Is the voltage greater than 10-12 volts?

Yes
The TBC (Trailer Brake Control) module is operating correctly. SEND the trailer to an authorized camper/trailer repair center.

No
GO to A4.

A4 CHECK THE TBC (Trailer Brake Control) MODULE PWM (Pulse Width Modulated) OUTPUT CIRCUIT FOR AN OPEN

- Ignition OFF.

- Disconnect: Trailer Tow C4099.

- Disconnect: TBC (Trailer Brake Control) Module C2142.

- Measure the resistance between trailer tow C4099-3, circuit CAT19 (BU), harness side and TBC (Trailer Brake Control) module C2142-14, circuit CAT19 (BU), harness side.





Is the resistance less than 5 ohms?

Yes
GO to A5.

No
REPAIR circuit CAT19 (BU) for an open circuit. TEST the system for normal operation.

A5 CHECK FOR CORRECT TBC (Trailer Brake Control) MODULE OPERATION

- Disconnect the TBC (Trailer Brake Control) module connector.

- Check for:
- corrosion

- damaged pins

- pushed-out pins


- Connect the TBC (Trailer Brake Control) module connector and make sure that it seats correctly.

- Operate the system and verify the concern is still present.

Is the concern still present?

Yes
INSTALL a new TBC (Trailer Brake Control) module. REFER to Trailer Brake Control (TBC) Module . TEST the system for normal operation.

No
The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector.