Pinpoint Test C: The Message Center Displays Wiring Fault On Trailer
Auxiliary Brake System - Trailer Brake Control (TBC) Module
Pinpoint Tests
Pinpoint Test C: The Message Center Displays WIRING FAULT ON TRAILER
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, 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 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 pin 3 of the 7-pin trailer tow connector. When the trailer is connected to the vehicle the Instrument Panel Cluster (IPC) should show the TRAILER CONNECTED message. If the WIRING FAULT ON TRAILER message is only displayed when the trailer is connected the fault is with the trailer wiring.
Every 4 seconds (when not braking) the TBC module sends a voltage pulse to pin 3 of the 7-pin trailer tow connector to determine whether or not a trailer is connected.
- DTC C2806 (Trailer Brake Output Circuit Short to Vbatt) - sets when the TBC module detects that the battery voltage is greater than 9 volts while not braking. The TBC module shuts off the trailer brake output and then shuts down.
- DTC C2807 (Trailer Brakes Wiring Circuit Short to Ground) - sets when the TBC module detects that the battery voltage drops by more than 20 percent during a braking event or the trailer brakes are drawing more than 28 amps. The TBC module shuts off the trailer brake output and then shuts down.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- TBC module
- Trailer
PINPOINT TEST C: THE MESSAGE CENTER DISPLAYS WIRING FAULT ON 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.
NOTE: Make sure the trailer brakes are electric-magnet actuated drum type brakes before proceeding with this pinpoint test.
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C1 CHECK THE MESSAGE IN THE MESSAGE CENTER
- Verify that a trailer is not connected to the trailer tow connector.
- Ignition ON.
- Allow the TBC module time to wake up and prove out.
- Observe the message center.
- Does the message center display WIRING FAULT ON TRAILER?
Yes
GO to C2.
No
SEND the trailer to an authorized camper/trailer repair facility.
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C2 CHECK THE TRAILER TOW CONNECTOR
- Ignition OFF.
- Disconnect: Trailer Tow C4099 .
- Check C4099 and the 7-pin trailer tow connector for:
- water intrusion
- corrosion
- pushed-out pins
- spread terminals
- Are the connectors OK?
Yes
GO to C3.
No
REPAIR the affected connector(s). CLEAR any DTCs present. TEST the system for normal operation.
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C3 CHECK THE TBC MODULE FOR DTCs
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: TBC Module Self Test .
- Clear the DTCs.
- Ignition OFF.
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: TBC Module Self Test .
- Apply vehicle brakes, release vehicle brakes, carry out the TBC module self-test.
- Does DTC C2806 return?
Yes
GO to C5.
No
If DTC C2807 returns,GO to C4. For all other DTCs, GO to the Trailer Brake Control (TBC) Module DTC Chart. Diagnostic Trouble Code Tests and Associated Procedures
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C4 CHECK THE TBC MODULE PWM OUTPUT CIRCUIT FOR A SHORT TO GROUND
- Ignition OFF.
- Disconnect: TBC Module C2142 .
- Measure the resistance between C4099-3, circuit CAT19 (BU), harness side and ground.
- Is the resistance greater than 10,000 ohms?
Yes
GO to C6.
No
REPAIR circuit CAT19 (BU) for a short to ground. TEST the system for normal operation.
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C5 CHECK THE TBC MODULE PWM OUTPUT CIRCUIT FOR A SHORT TO VOLTAGE
- Ignition OFF.
- Disconnect: TBC Module C2142 .
- Ignition ON.
- Measure the voltage between C4099-3, circuit CAT19, (BU), harness side and ground while operating the following lamps in turn:
- Parking lamps
- Stop lamps
- Reversing lamps
- Is any voltage present?
Yes
REPAIR circuit CAT19 (BU) for a short to power. TEST the system for normal operation.
No
GO to C6.
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C6 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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