Lost Communication With Restraints System Sensor B
Your vehicle's computer lost connection with a sensor that monitors the airbag and safety restraint system. It's like a phone losing signal from a tower—the system can't hear what the sensor is saying.
The ECU communicates with Restraints System Sensor B via a serial data bus to monitor sensor status and signal integrity. The ECU expects periodic valid messages within a specific timeframe; if communication is lost for a set duration, a fault is logged.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Bus Signal Timeout | Valid message every 10-100ms | No valid message received for >500ms |
| Signal Voltage | 0.5-4.5V on CAN bus | <0.2V or >5V indicates open/short circuit |
Code U0171 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, U0171 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.