U0137

Universal

Lost Communication With Trailer Brake Control Module

Definition source: General OBD-II reference catalog
Definition verification: Not independently verified for display.
Time: Varies by diagnosis and vehicle | Diagnostic difficulty: Medium
High Severity

The vehicle has detected that it cannot communicate with the trailer brake control module. That module helps manage braking for a connected trailer. Depending on the vehicle and trailer setup, trailer braking may be unavailable or limited, though an intermittent communication issue or a vehicle without a connected trailer may produce no noticeable symptoms.

Report an error with this code

⚠️ Before You Begin (Safety First)

If you are towing and the trailer brake warning is on, or trailer braking seems absent or abnormal, stop somewhere safe and do not continue towing until the braking system has been checked. The vehicle may still brake normally, but trailer braking could be impaired.

Common Symptoms

  • A trailer brake warning or message may appear if the vehicle detects that the module is unavailable.
  • Trailer brakes may not respond, or may operate abnormally, if communication loss prevents the system from controlling them.
  • A trailer brake indicator or related feature may be unavailable.
  • There may be no noticeable symptoms if the issue is intermittent or the vehicle is not using a trailer brake system.

Common Causes

  • A loose, damaged or corroded connector or wiring may interrupt communication with the trailer brake control module.
  • A problem with the module's power supply or ground may prevent it from operating or communicating.
  • A fault elsewhere on the vehicle communication network may interrupt messages to or from the module.
  • Low or unstable vehicle voltage may contribute to a temporary communication loss.
  • The trailer brake control module itself may have a fault, but this code alone does not prove that it has failed.

Diagnostic Steps

  1. If towing, check whether the trailer brake warning is present and whether trailer braking behaves normally. Stop towing if braking is absent or abnormal.
  2. Check the vehicle owner's manual for any trailer brake system warnings or recommended basic checks that apply to your vehicle.
  3. With the vehicle safely parked, visually inspect accessible trailer brake wiring and connectors for looseness, visible damage or corrosion. Do not pull on wires or disconnect components unless the owner's manual permits it.
  4. Check relevant fuses only as described in the owner's manual, and replace a blown fuse only with the specified type. If it blows again, have the circuit diagnosed.
  5. If the warning persists or returns, arrange a scan of the vehicle's modules and electrical system rather than replacing the control module based on this code alone.

When to Call a Professional

A technician can scan relevant modules for communication faults, then check the trailer brake module's power and ground, connectors, wiring and vehicle network communication. The code alone does not establish that the module needs replacement; exact tests and procedures depend on the vehicle.

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Commonly Asked Questions

Does U0137 prove the trailer brake control module has failed?

No. It indicates lost communication with the module. Wiring, connectors, power, ground, vehicle voltage or another network fault may also cause the condition.

Can I drive the vehicle with this code?

The code concerns communication with the trailer brake control module, so the key safety concern is towing. Do not continue towing if trailer braking is unavailable or abnormal. If you are not towing, follow any vehicle warnings and arrange diagnosis.

Why might there be no symptoms?

The communication loss may be intermittent, or the trailer brake system may not be in use. A warning may still appear, so check the vehicle's messages and have a persistent code diagnosed.

Should I replace the module first?

No. A technician should check module power and ground, connectors, wiring and network communication before deciding whether the module itself is faulty.

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