Pinpoint Test B: The Trailer Brakes are Inoperative
Auxiliary Brake System - Trailer Brake Control (TBC) Module
Pinpoint Tests
Pinpoint Test B: The Trailer Brakes are Inoperative
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, 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 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 module receives stoplamp switch information from the PCM and information from the ABS module over the High Speed Controller Area Network (HS-CAN). If there is a problem in the ABS module that is preventing this information from being sent to the TBC module, the TBC module enters a limited operating mode. The TBC module receives fused battery voltage from Battery Junction Box (BJB) fuse 17 (30A) and fused ignition voltage from Body Control Module (BCM) fuse 37 (10A).
This pinpoint test is intended to diagnose the following:
- Fuse(s)
- Wiring, terminals or connectors
- Trailer tow connector
- TBC module
- Customer trailer
PINPOINT TEST B: 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.
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B1 CHECK FOR ANY PCM DTCs
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: PCM Key ON Engine OFF (KOEO) Self-Test.
- Retrieve and record any PCM DTCs.
- Are any PCM DTCs retrieved?
Yes
REFER to Electronic Engine Controls Testing and Inspection.
No
GO to B2.
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B2 CHECK FOR ANY ABS MODULE DTCs
- Enter the following diagnostic mode on the scan tool: ABS Module Self-Test.
- Retrieve and record any ABS module DTCs.
- Are any ABS module DTCs retrieved?
Yes
REFER to Vehicle Dynamic Systems Testing and Inspection.
No
GO to B3.
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B3 CHECK FOR SCAN TOOL COMMUNICATION WITH THE TBC MODULE
- Enter the following diagnostic mode on the scan tool: Network Test.
- Carry out the network test.
- Did the TBC module pass the network test?
Yes
GO to B4.
No
REFER to Module Communications Network Testing and Inspection.
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B4 CHECK FOR TBC MODULE DTCs
- Review the DTCs retrieved and recorded during TBC module self-test.
- Are any TBC module DTCs present?
Yes
REFER to the Trailer Brake Control (TBC) Module DTC Chart. Diagnostic Trouble Code Tests and Associated Procedures
No
GO to B5.
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B5 CHECK THE TBC MODULE FOR MAXIMUM OUTPUT
NOTE: Battery voltage must be greater than 10 volts.
- Ignition ON.
- Set a gain of 10 in the TBC module.
- NOTE: If the manual slider switch is held to the full left position for more than 5 minutes, the TBC module automatically shuts down.
- Have an assistant press the manual slider switch fully to the left with a gain of 10 on the TBC module.
- Measure the voltage between trailer tow 7-pin trailer tow connector electric brake supply pin, component side and ground.
- Is the voltage greater than 10-12 volts?
Yes
The TBC module is operating correctly. SEND the trailer to an authorized camper/trailer repair center for an overload condition.
No
GO to B6.
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B6 CHECK THE TRAILER TOW CONNECTOR FOR AN OPEN
- Ignition OFF.
- Disconnect: Trailer Tow Connector C439A.
- Ignition ON.
- Have an assistant press the manual slider switch fully to the left with a gain of 10 on the TBC module.
- Measure the voltage between the trailer tow connector C439A-3, circuit CAT19 (BU), harness side and ground.
- Is the voltage greater than 10 volts?
Yes
INSTALL a new trailer tow connector. CLEAR the DTCs. TEST the system for normal operation.
No
GO to B7.
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B7 CHECK THE TBC MODULE PWM OUTPUT CIRCUIT FOR AN OPEN
- Ignition OFF.
- Measure the resistance between the trailer tow connector C439A-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 B8.
No
REPAIR circuit CAT19 (BU). TEST the system for normal operation.
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B8 CHECK TBC MODULE CIRCUIT SBB17 (RD) FOR VOLTAGE
- Ignition OFF.
- Measure the voltage between TBC module C2142-8, circuit SBB17 (RD), harness side and ground.
- Is the voltage greater than 10 volts?
Yes
VERIFY the BJB fuse 17 (20A) is OK. If OK, REPAIR circuit SBB17 (RD) for an open. TEST the system for normal operation.
No
GO to B9.
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B9 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 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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