Pinpoint Test AD: The Trailer Electric Brakes Are Inoperative/Always Applied
Trailer Lamps
Pinpoint Tests
Pinpoint Test AD: The Trailer Electric Brakes Are Inoperative/Always Applied
Refer to Wiring Diagram Set 95, Trailer/Camper Adapter for schematic and connector information. Diagrams By Number
Normal Operation
The Trailer Brake Control (TBC) module is provided voltage at all times by the Battery Junction Box (BJB) fuse 17 (30A). The TBC module receives a voltage signal from the stoplamp switch when the brake pedal is applied. When requested, the TBC module provides voltage to the trailer tow connector.
This pinpoint test is intended to diagnose the following:
- Fuse
- Wiring, terminals or connectors
- TBC module
- Trailer tow connector
- Trailer
PINPOINT TEST AD: THE TRAILER ELECTRIC BRAKES ARE INOPERATIVE/ALWAYS APPLIED
NOTICE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
NOTE: Before beginning diagnostics, visually inspect the trailer tow connector for signs of corrosion or damage. Repair or install a new trailer tow connector as required.
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AD1 CHECK FOR VOLTAGE TO THE TRAILER TOW CONNECTOR (INOPERATIVE CONDITION)
- Ignition OFF.
- Disconnect the trailer from the vehicle.
- Set the gain on the TBC module to the maximum setting.
- While applying the brake pedal, measure the voltage between the trailer tow connector pin 3, circuit CAT19 (BU), component side and ground.
- Is the voltage greater than 10 volts?
Yes
GO to AD8.
No
GO to AD2.
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AD2 CHECK THE TRAILER TOW CONNECTOR
- Disconnect: Trailer Tow C473.
- While applying the brake pedal, measure the voltage between the trailer tow C473-3, circuit CAT19 (BU), harness side and ground.
- Is the voltage greater than 10 volts?
Yes
INSTALL a new trailer tow connector. TEST the system for normal operation.
No
GO to AD3.
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AD3 CHECK FOR VOLTAGE TO THE TBC MODULE
- Disconnect: TBC Module C239.
- Measure the voltage between the TBC module C239-1, circuit SBB17 (RD), harness side and ground.
- Is the voltage greater than 10 volts?
Yes
GO to AD4.
No
VERIFY the BJB fuse 17 (30A) is OK. If OK, REPAIR circuit SBB17 (RD) for an open. TEST the system for normal operation. If not OK, REFER to the Wiring Diagrams to identify the possible causes of the circuit short. Diagrams By Number
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AD4 CHECK THE BRAKE PEDAL INPUT TO THE TBC MODULE
- While applying the brake pedal, measure the voltage between the TBC module C239-2, circuit CCB08 (VT/WH), harness side and ground.
- Is the voltage greater than 10 volts?
Yes
GO to AD5.
No
REPAIR circuit CCB08 (VT/WH) for an open. TEST the system for normal operation.
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AD5 CHECK FOR VOLTAGE TO THE TBC MODULE USING THE CONNECTOR GROUND
- Measure the voltage between the TBC module C239-1, circuit SBB17 (RD), harness side and the TBC module C239-6, circuit GD138 (BK/WH), harness side.
- Is the voltage greater than 10 volts?
Yes
GO to AD6.
No
REPAIR circuit GD138 (BK/WH) for an open. TEST the system for normal operation.
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AD6 CHECK THE TBC MODULE OUTPUT CIRCUIT FOR A SHORT TO GROUND
- Measure the resistance between the TBC module C239-3, circuit CAT19 (BU), harness side and ground.
- Is the resistance greater than 10,000 ohms?
Yes
GO to AD7.
No
REPAIR circuit CAT19 (BU) for a short to ground. TEST the system for normal operation.
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AD7 CHECK THE TBC MODULE OUTPUT CIRCUIT FOR AN OPEN
- Measure the resistance between the TBC module C239-3, circuit CAT19 (BU), harness side and the trailer tow C473-3, circuit CAT19 (BU), harness side.
- Is the resistance less than 5 ohms?
Yes
INSTALL a new TBC module. TEST the system for normal operation.
No
REPAIR circuit CAT19 (BU) for an open. TEST the system for normal operation.
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AD8 CHECK FOR VOLTAGE TO THE TRAILER TOW CONNECTOR (DOES NOT OPERATE CORRECTLY)
- With the brake pedal released, measure the voltage between the trailer tow connector pin 3, circuit CAT19 (BU), component side and ground.
- Is any voltage present?
Yes
GO to AD9.
No
The vehicle is operating correctly. SEND the trailer to an authorized camper/trailer repair facility.
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AD9 CHECK THE TBC MODULE OUTPUT CIRCUIT FOR A SHORT TO VOLTAGE
- Disconnect: TBC Module C238.
- Measure the voltage between the trailer tow connector pin 3, circuit CAT19 (BU), component side and ground.
- Is any voltage present?
Yes
REPAIR circuit CAT19 (BU) for a short to voltage. TEST the system for normal operation.
No
INSTALL a new TBC module. TEST the system for normal operation.
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