U0671Lost Communication With Fuel Temperature Sensor B
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- Sensor B is the second SENT temperature sensor in GM's high-pressure fuel rail (sensor 2 in 25OBDG03A and 25OBDG03B). Its link test mirrors that of sensor A, line stuck high with too few pulses, 400 of 500 samples at 6.25 ms, Type A. What sets B apart is its job: GM compares it with sensor 1 and stores P111F when the two differ by more than 10 °C in 100 of 125 samples, and it checks the raw digital value of sensor 2 against limits below 145 and above 1,865 counts (P0187/P0188, Type B). Without B both checks go blind, so a drifting sensor A could go unnoticed. If U0670 and U0671 appear together, look first at a shared connector, supply or ground; if only B is missing, its own branch or sensor is more likely.
- What you may notice
- Check engine light
- Sensor comparison and range checks of sensor B not completed
- Often no drivability complaint
- Likely causes
- LikelySignal wire of sensor B chafed, shorted or open
- PossibleShared 5 V supply or ground of both rail sensors faulty
- PossibleFuel temperature sensor B defective
- RareEngine controller input or software fault
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €60 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.