U0137 indicates the vehicle's main computer (PCM or BCM) has lost communication with the Trailer Brake Control Module (TBCM). This is a network communication fault, not a failure of the vehicle's primary braking system. The code typically points to a wiring, connection, or module issue rather than the main engine computer.
The TBCM itself has failed and no longer responds on the network. This is the most common actual component failure causing this code.
Wires to the TBCM are broken, chafed, or shorted due to routing near moving parts, corrosion, or age. The trailer tow wiring is exposed to the elements.
Oxidation, corrosion, or loose pins at the TBCM connector or the body control module (BCM) connector can break communication. Moisture intrusion is common.
A blown fuse or failed relay that supplies power to the trailer brake circuit will cause loss of communication and module failure.
The BCM often serves as the gateway for trailer-related communications. If the BCM has failed or has software issues, it may not communicate with the TBCM.
A more general fault on the vehicle's communication network (CAN bus) could affect multiple modules including the TBCM. Usually accompanied by other U-codes.
The vehicle's primary brakes are unaffected. However, trailer brakes will not function, so towing a trailer is unsafe and may be illegal.
No. This code indicates a real fault in the communication circuit. The underlying cause will not self-correct and requires diagnosis.
No. While some may recommend PCM replacement, it is very rarely the cause of U0137. The trailer brake module itself, its wiring, or connections are the actual problem in the vast majority of cases. PCM replacement for this code is almost always unnecessary and expensive.
A standard OBD-II scan tool can read the U0137 code, but accessing the Trailer Brake Control Module specifically may require a more advanced diagnostic tool or dealer-level equipment to view module-specific data.