U0671 code meaning
Lost Communication With Fuel Temperature Sensor B
Network system Generic code U06xx codes Check engine light
What U0671 means
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.
U0671 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0671
- Check engine light
- Sensor comparison and range checks of sensor B not completed
- Often no drivability complaint
Common causes of U0671
- Most 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
- Less likelyEngine controller input or software fault
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Fuel temp sensor bVehicle bus wiring
What each part of U0671 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 71 | The exact fault in that area. |
What to do next
- Note U0671 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0671
What does U0671 mean?
U0671 means "Lost Communication With Fuel Temperature Sensor B". Sensor B is the second SENT temperature sensor in GM's high-pressure fuel rail (sensor 2 in 25OBDG03A and 25OBDG03B). It is a generic code, so it means the same on every make.
Is it safe to drive with U0671?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will U0671 fail an emissions test?
Yes, it can. U0671 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U0671 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2 hours of work. This is a job for a workshop.
Will U0671 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.