Pinpoint Test B: The Trailer Brakes are Always Engaged
Auxiliary Brake System - Trailer Brake Control (TBC) Module
Pinpoint Tests
Pinpoint Test B: The Trailer Brakes are Always Engaged
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 provided to the trailer is varied with a Pulse Width Modulated (PWM) signal that switches between 0 volts and battery voltage, according to the Trailer Brake Control (TBC) module gain setting, the higher the duty cycle the more braking power available. 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 pin 3 of the 7-pin trailer tow connector. The TBC module also receives information from the brake pressure switch (also called the speed control deactivation switch) and the stoplamp switch from the PCM over the High Speed Controller Area Network (HS-CAN) bus.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- TBC module
- Trailer
PINPOINT TEST B: THE TRAILER BRAKES ARE ALWAYS ENGAGED
NOTICE: Use the Flex Probe Kit for all test connections to prevent damage to the wiring terminals. Do not use standard multi-meter probes.
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B1 CHECK FOR ANY TBC MODULE OR PCM DTCs
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: TBC Module Self Test .
- Enter the following diagnostic mode on the scan tool: PCM Self Test .
- Retrieve and record any TBC module or PCM DTCs.
- Are any TBC module or PCM DTCs retrieved?
Yes
For TBC module DTCs, REFER to DTC Chart Diagnostic Trouble Code Tests and Associated Procedures. For PCM DTCs, REFER to Electronic Engine Controls P Codes for Electronic Engine Controls.
No
GO to B2.
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B2 OBSERVE THE VEHICLE STOPLAMP OPERATION
- Monitor the vehicle stoplamps while pressing and releasing the brake pedal.
- Do the vehicle stoplamps operate correctly?
Yes
GO to B3.
No
REFER to Exterior Lighting Testing and Inspection to diagnose the stoplamp switch.
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B3 CHECK THE TBC MODULE OUTPUT
NOTE: Every 4 seconds a voltage pulse is applied as a trailer connectivity test.
- Ignition OFF.
- Disconnect: Trailer Tow C4099 .
- Ignition ON.
- Make sure the brake pedal is not pressed and the manual slider switch is not being applied.
- Measure the voltage between trailer tow C4099-3, circuit CAT19 (BU), harness side and ground.
- Is steady voltage indicated?
Yes
GO to B4.
No
The TBC module and vehicle wiring are operating correctly. SEND the trailer to an authorized camper/trailer repair facility.
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B4 CHECK THE TBC MODULE PWM OUTPUT CIRCUIT FOR A SHORT TO VOLTAGE
- Ignition OFF.
- Disconnect: TBC Module C2142 .
- Ignition ON.
- Measure the voltage between trailer tow C4099-3, circuit CAT19 (BU), harness side and ground.
- Is any voltage present?
Yes
REPAIR circuit CAT19 (BU) for a short to voltage. TEST the system for normal operation
No
GO to B5.
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B5 CHECK FOR CORRECT TBC MODULE OPERATION
- Disconnect the TBC module connector.
- Check for:
- corrosion
- damaged pins
- pushed-out pins
- Connect the TBC 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 module. REFER to Trailer Brake Control (TBC) Module Service and Repair. 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.
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