Pinpoint Test E: The Trailer Brakes are Always Engaged and/or The Message Center Intermittently Displays TRAILER DISCONNECTED o
Auxiliary Brake System - Trailer Brake Control (TBC) Module
Pinpoint Tests
Pinpoint Test E: The Trailer Brakes are Always Engaged and/or The Message Center Intermittently Displays TRAILER DISCONNECTED or WIRING FAULT ON TRAILER While Towing a Trailer
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 that switches between 0 volt 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 greater than 10-12 volts supplied to trailer tow C4099-3 circuit CAT19 (BU). The TBC module receives brake pressure information from the ABS module and Brake Pedal Position (BPP) (stoplamp) switch information from the PCM, both over the High Speed Controller Area Network (HS-CAN) bus.
This pinpoint test is intended to diagnose the following:
- Fuse(s)
- Wiring, terminals or connectors
- TBC module
PINPOINT TEST E: THE TRAILER BRAKES ARE ALWAYS ENGAGED AND/OR THE MESSAGE CENTER INTERMITTENTLY DISPLAYS TRAILER DISCONNECTED OR WIRING FAULT ON TRAILER WHILE TOWING A TRAILER
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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E1 CHECK FOR TBC MODULE DTCs
- Review the DTCs retrieved and recorded during Inspection and Verification.
- Are any TBC module DTCs present?
Yes
GO to the Trailer Brake Control (TBC) Module DTC Chart. Trailer Brake Control (TBC) Module DTC Chart
No
GO to E2.
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E2 CHECK THE TBC BRAKE ON/OFF (BOO_TBC) PID
- Connect the scan tool.
- Ignition OFF.
- Enter the following diagnostic mode on the scan tool: DataLogger - TBC Module .
- Monitor the BOO_TBC PID while pressing and releasing the brake pedal.
- Does the PID agree with the brake pedal position?
Yes
GO to E4.
No
GO to E3.
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E3 CHECK THE PCM BOO PID
- Enter the following diagnostic mode on the scan tool: DataLogger - PCM .
- Monitor the BOO PID while pressing and releasing the brake pedal.
- Does the PID agree with the brake pedal position?
Yes
REFER to Module Communications Network Testing and Inspection to diagnose the HS-CAN bus.
No
REFER to Exterior Lighting Testing and Inspection to diagnose the stoplamp (BPP) switch.
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E4 CHECK THE TBC MODULE OUTPUT
NOTE: Every 4 seconds a voltage pulse is applied as a trailer connectivity test.
- Ignition ON.
- Make sure the brake pedal is not pressed and the manual slider switch is not being applied.
- Measure the voltage between 7-pin trailer tow connector pin-3, circuit CAT19 (BU), harness side and ground.
- Is the voltage approximately 0.3-0.5 volt?
Yes
The TBC module and vehicle wiring are operating correctly. SEND the trailer to an authorized camper/trailer repair center.
No
GO to E5.
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E5 CHECK THE TBC MODULE PWM OUTPUT CIRCUIT FOR A SHORT TO VOLTAGE
- Ignition OFF.
- Disconnect: TBC Module C2142 .
- Ignition ON.
- Measure the voltage between 7-pin trailer tow connector pin-3, circuit CAT19 (BU), harness side and ground.
- Is any voltage present?
Yes
REPAIR circuit CAT19 (BU). TEST the system for normal operation.
No
GO to E6.
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E6 CHECK FOR CORRECT TBC MODULE OPERATION
- Check the TBC module connector for:
- corrosion.
- pushed-out pins.
- spread terminals.
- Connect: TBC Module C2142 .
- Make sure the connector is seated correctly, then 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. CLEAR the DTCs. REPEAT the self-test.
No
The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test.
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