Lost Communication With Trailer Brake Control Module
Your truck's main computer has lost its connection to the trailer brake control module, like a phone losing signal to a Bluetooth device. The system can't communicate brake commands to the trailer, which is a safety issue.
The ECU continuously monitors CAN bus communication signals from the trailer brake control module at regular intervals. If the expected message is not received within a specific timeout window (typically 100-500ms), the ECU registers a lost communication fault. The module expects periodic heartbeat signals confirming the trailer brake system is active and responsive.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| CAN Bus Message Timeout | Message received every 100-500ms | No message for >500ms or corrupted signal |
| Module Response Signal | Valid voltage/signal present | Signal loss or invalid data pattern |
Code U0137 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, U0137 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.