Pinpoint Test C: The Message Center Displays Trailer Fault
Auxiliary Brake System - Trailer Brake Control (TBC) Module
Pinpoint Tests
Pinpoint Test C: The Message Center Displays TRAILER FAULT
NOTE: Carry out all pinpoint tests without a trailer connected to the vehicle. Pinpoint Tests
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 pin 3 of trailer tow connector C4099 along circuit CAT19 (BU).
When there is no input from the stoplamp switch or manual slider lever, the TBC module continually sends a low voltage (approximately 0.3 volt) along circuit CAT19 (BU) to pin-3 of the 7-pin trailer tow connector. Then, once every 4 seconds, this voltage is momentarily increased (approximately 0.5 volt) to determine whether or not a trailer is connected.
The factory 7-pin trailer tow connector is attached with a bracket to the rear bumper of the vehicle or to the trailer hitch (if equipped). The 7-pin trailer tow connector acts as a jumper connection between C4099 (female) and the trailer electrical connector (female).
- DTC C2806 (Trailer Brakes Wiring Circuit Short to Voltage) If the TBC module output along circuit CAT19 (BU) is equal to or greater than 9 volts while not braking for 200 ms or more, the TBC module sends the TRAILER FAULT message to the Instrument Cluster (IC), shuts off trailer brake output and then shuts down.
- DTC C2807 (Trailer Brakes Wiring Circuit Short to Ground) If battery voltage drops by more than 20% for 200 ms or more during a braking event, or for 1.5 ms or more during an on-demand self test, the TBC module sends the TRAILER FAULT message to the IC, shuts off trailer brake output and then shuts down. This DTC can also be set if the trailer brakes draw more than 28 amps for 20 ms or more.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- TBC module
- Customer trailer
PINPOINT TEST C: THE MESSAGE CENTER DISPLAYS TRAILER FAULT
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 OFF.
- Allow the TBC module time to wake up and prove out.
- Observe the message center.
- Does the message center display TRAILER FAULT?
Yes
GO to C2.
No
SEND the trailer to an authorized camper/trailer repair center.
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C2 CHECK THE TRAILER TOW CONNECTOR
- Ignition OFF.
- Disconnect the 7-pin trailer tow connector from C4099 and inspect both connectors for:
- water intrusion.
- corrosion.
- pushed-out pins.
- spread terminals.
- Is the connector OK?
Yes
CONNECT the 7-pin trailer tow connector to C4099. GO to C3.
No
REPAIR the affected connector(s). CLEAR the DTCs. REPEAT the self-test.
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C3 CHECK THE TBC MODULE ON-DEMAND DTCs
- Connect the scan tool.
- Ignition ON.
- Using the scan tool, clear the DTCs.
- Ignition OFF.
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: Self Test - TBC Module.
- Does DTC C2806 or C2807 return?
Yes
For DTC C2806, GO to C5.
For DTC C2807, GO to C4.
No
For all other DTCs, GO to the Trailer Brake Control (TBC) Module DTC Chart. Diagnostic Trouble Code Tests and Associated Procedures
If no DTCs returned, the TBC module and vehicle wiring are operating correctly. SEND the trailer to an authorized camper/trailer repair center.
CLEAR the DTCs. REPEAT the self-test.
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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 7-pin trailer tow connector pin-3, circuit CAT19 (BU), harness side and ground.
- Is the resistance greater than 10,000 ohms?
Yes
GO to C7.
No
REPAIR circuit CAT19 (BU). CLEAR the DTCs. REPEAT the self-test.
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C5 CHECK THE TBC MODULE OUTPUT
NOTE: Every 4 seconds a voltage pulse is applied as a trailer connectivity test.
- 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
GO to C7.
No
GO to C6.
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C6 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.
- Measure the voltage between 7-pin trailer tow connector pin-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). CLEAR the DTCs. REPEAT the self-test.
No
The system is operating correctly at this time. INSPECT the 7-pin trailer tow connector for evidence of water intrusion or corrosion. INSPECT the trailer tow C439A harness for evidence of chaffed wiring or improper wire repair. REPAIR wiring as necessary. CLEAR the DTCs. REPEAT the self-test.
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C7 CHECK THE TBC MODULE FOR MAXIMUM OUTPUT
NOTE: Battery voltage must be greater than 10 volts.
- Ignition OFF.
- Connect: TBC Module C2142.
- Ignition ON.
- Input a gain setting of 10 into the TBC module.
- NOTE: If the manual slider switch is held to the full left position for more than 5 minutes, the TBC module will automatically shut down.
- Have an assistant press the manual slider switch fully to the left with a gain of 10 on the TBC module.
- Measure voltage between 7-pin trailer tow connector pin-3, circuit CAT19 (BU), harness side and ground.
- Is the voltage greater than 10-12 volts?
Yes
The system is operating correctly at this time. INSPECT the 7-pin trailer tow connector for evidence of water intrusion or corrosion. INSPECT the trailer tow C4099 harness for evidence of chaffed wiring or improper wire repair. REPAIR wiring as necessary. CLEAR the DTCs. REPEAT the self-test.
No
GO to C8.
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C8 CHECK THE TBC MODULE PWM OUTPUT CIRCUIT FOR AN OPEN
- Ignition OFF.
- Disconnect: TBC Module C2142.
- Measure resistance between 7-pin trailer tow connector pin-3, circuit CAT19 (BU), harness side and TBC module C2142-14, circuit CAT19 (BU), harness side.
- Is the resistance less than 5 ohms?
Yes
GO to C9.
No
REPAIR circuit CAT19 (BU). CLEAR the DTCs. REPEAT the self-test.
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C9 CHECK FOR CORRECT TBC MODULE OPERATION
- Disconnect: TBC Module C2142.
- Check the 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. INSPECT the 7-pin trailer tow connector for evidence of water intrusion or corrosion. INSPECT the trailer tow C439A harness for evidence of chaffed wiring or improper wire repair. REPAIR wiring as necessary. CLEAR the DTCs. REPEAT the self-test.
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