Lost Communication With Restraints Control Module
Your car's main computer can't talk to the airbag control module, like a radio station losing its signal. This communication failure means the airbag system can't receive commands and may not deploy in a crash.
The ECM continuously monitors the CAN bus communication link to the Restraints Control Module (RCM) by sending periodic heartbeat messages and expecting acknowledgment responses. Loss of communication occurs when these acknowledgments fail or the expected signal voltage/timing falls outside normal parameters for a calibrated threshold period.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| CAN Bus Message Response Time | < 100 ms round trip | > 500 ms or no response for > 2 seconds |
| RCM Signal Voltage | 0.5 - 4.5V on CAN lines | < 0.5V or > 5.5V indicating open/short circuit |
Code U0151 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, U0151 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.