Lost Communication With Restraints System Sensor C
Your car's computer has lost the radio signal from a safety sensor that helps deploy airbags and seatbelt tensioners. Think of it like a walkie-talkie losing connection with one of its partners.
The ECU constantly checks for valid CAN bus messages from Restraint System Sensor C, which monitors crash severity and occupant position. If no valid signal is received within a defined time window, the ECU logs this fault code.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| CAN Message Response Time | < 100 milliseconds | > 500 milliseconds or no response |
| Signal Voltage | 4.5V - 5.5V | < 3V or > 6V |
Code U0172 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, U0172 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.