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
Information only
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What U0137 means

U0137 is stored when the body or chassis control module -- or another gateway module -- loses CAN bus communication with the Running Board Control Module (RBCM). Power running boards are motorised side steps that automatically deploy when a door is opened and retract when the door closes. Their dedicated control module manages motor direction, position feedback, and obstacle detection, exchanging state messages with the BCM or door modules over the serial data bus.

Because the running boards are a comfort and convenience feature rather than a safety-critical or emissions-related system, U0137 typically illuminates the MIL or a warning lamp at low priority and does not affect engine operation or powertrain control. The boards may default to the deployed position (extended) or become inoperative depending on the failsafe strategy employed by the manufacturer.

Diagnosis should start with supply-voltage verification at the RBCM, since these modules are mounted in the rocker-panel area and are exposed to road spray, ice, and mechanical damage. Terminal corrosion and chafed harness wires near the door hinge area are frequent causes. CAN bus termination checks are worthwhile when multiple U-codes are present simultaneously.

Common causes

Most-frequently reported root causes when U0137 is logged.

  • 1
    Corroded or damaged harness connector at the Running Board Control Module due to road-spray exposure.
  • 2
    Chafed or broken data bus wire in the door-hinge or rocker-panel routing area.
  • 3
    Water intrusion into the RBCM housing causing internal corrosion.
  • 4
    Blown supply fuse or open ground circuit for the RBCM.
  • 5
    Failed RBCM hardware (motor driver or microcontroller fault).
  • 6
    CAN bus fault on a shared network segment affecting multiple modules simultaneously.

Symptoms drivers notice

MIL or body warning lamp illuminated.
Power running boards inoperative -- do not deploy or retract.
Running boards may remain in the deployed (extended) position permanently.
No other drivability or powertrain symptoms.

How to diagnose U0137

A typical diagnostic flow when this code is present.

  1. 1
    Record all DTCs and note whether other U-codes are present indicating a broader bus fault.
  2. 2
    Physically inspect the running board module and its harness for signs of moisture, corrosion, or mechanical damage.
  3. 3
    Verify ignition-switched supply voltage and ground continuity at the RBCM connector.
  4. 4
    Check the relevant fuse(s) in the body fuse box for the running board circuit.
  5. 5
    Measure CAN bus differential voltage at the RBCM connector with a multimeter to check for bus activity.
  6. 6
    Repair any wiring or connector fault found; clear codes and retest board operation.
  7. 7
    If wiring is sound, replace the RBCM and verify communication is restored.

Related network codes

Frequently asked questions

Is U0137 dangerous to drive with?

The code itself does not affect engine or braking systems. However, if the running boards are stuck in the deployed position, they may strike kerbs or road obstacles, so it is prudent to have the fault repaired promptly.

Why is this code set even if the running boards seem to work?

Intermittent bus dropouts caused by a marginal connection can set the code in memory even if the boards operated normally at that moment. The fault may have cleared itself; a road test with a data logger can help catch intermittent faults.

Can cold weather trigger U0137?

Yes. Moisture trapped in the rocker-panel harness connector can freeze and temporarily open the circuit, setting U0137. The code may clear once temperatures rise and the connection re-establishes.

Will clearing the code make the running boards work again?

Clearing the code only removes the stored fault entry. If the underlying wiring or module fault persists, the code will return and the boards will remain inoperative.

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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