U0137

Lost Communication With Trailer Brake Control Module

U0137 is a generic OBD-II network diagnostic trouble code: Lost Communication With Trailer Brake Control Module. It is logged by the engine control unit when the network monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
U0137
Group
Network
System
Network
Severity
Warning (MIL on)
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What U0137 means

U0137 is stored when the body control module, another gateway module, or the ECM loses CAN bus communication with the Trailer Brake Control Module (TBCM). The trailer brake control module manages the integrated electronic trailer brake controller found on many trucks and tow vehicles, applying and modulating the trailer's electric or electric-over-hydraulic brakes in proportion to the tow vehicle's braking and reporting connection and gain status back over the serial data bus.

The DTC sets when the expected periodic message from the TBCM is absent for a calibrated timeout period. Because the trailer brake system is a safety-related towing feature, loss of communication typically disables integrated trailer braking and posts a Trailer Brake Module Fault warning. The tow vehicle itself continues to drive and brake normally, but a connected trailer will not receive proportional braking, reducing overall stopping capability while towing.

The most common causes are wiring faults on the twisted-pair data bus circuit between the vehicle and the TBCM, corroded or damaged connectors, and loss of power or ground to the module. Exposure to road salt and moisture can corrode terminals and create intermittent opens. Verify supply voltage, ground, and bus integrity at the TBCM connector before replacing the module.

Common causes

Most-frequently reported root causes when U0137 is logged.

  • 1
    Open or short in the CAN data bus wiring between the vehicle network and the trailer brake control module.
  • 2
    Corroded or damaged connector terminals at the TBCM harness connector.
  • 3
    Loss of power supply or blown fuse feeding the TBCM.
  • 4
    Poor or missing ground connection for the TBCM.
  • 5
    Water or road-salt intrusion causing corrosion in the module or connector.
  • 6
    Failed trailer brake control module internal hardware.
  • 7
    Bus fault on a shared segment affecting multiple modules simultaneously.

Symptoms drivers notice

MIL or a Trailer Brake Module Fault warning displayed.
Integrated trailer brake system disabled or inoperative.
No trailer braking or reduced trailer stopping power while towing.
Scan tool unable to communicate with the trailer brake control module.
Trailer brake gain and connection status unavailable on the driver display.

How to diagnose U0137

A typical diagnostic flow when this code is present.

  1. 1
    Record all DTCs and freeze-frame data, noting whether other U-codes indicate a broader bus fault.
  2. 2
    Inspect the trailer brake control module and its harness for moisture, corrosion, or mechanical damage.
  3. 3
    Verify ignition-switched supply voltage and ground continuity at the TBCM connector.
  4. 4
    Check the relevant fuse(s) for the trailer brake circuit in the fuse box.
  5. 5
    Measure CAN bus differential voltage or termination resistance at the TBCM connector to check bus integrity.
  6. 6
    Confirm whether the TBCM appears on the network using scan tool node diagnostics.
  7. 7
    If wiring and power are sound, reprogram or replace the TBCM and verify communication is restored.

Related network codes

Frequently asked questions

Is U0137 safe to drive with?

The tow vehicle drives and brakes normally, but with the trailer brake module offline a connected trailer will not brake properly, so it is unsafe to tow until the fault is repaired.

Why does U0137 sometimes set even when the trailer brakes seemed to work?

Intermittent bus dropouts from a marginal connection can log the code in memory even if the module operated normally at that moment; a road test with a data logger can help catch intermittent faults.

Can cold or wet weather trigger U0137?

Yes. Moisture or road salt trapped in a connector can freeze or corrode and temporarily open the circuit, setting U0137, which may clear once the connection re-establishes.

Will reprogramming the module fix U0137?

If the module responds but the code persists, flashing the latest TBCM firmware can sometimes clear it, but only after power, ground, and bus wiring have been confirmed good.

Disabling U0137 in software

RaceTune can permanently disable U0137 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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