What it means
The vehicle bus reports loss of communication with smart fuel level sensor B. Tank gauge may freeze and low-fuel warnings may be incorrect.
At a glance
- Usually lights the warning light of the system that lost communication
How it works
Smart fuel level sensor B measures fuel in its section of the tank and communicates its reading over the vehicle network. U0677 sets when the receiving module stops getting messages from sensor B, which can make the tank gauge or low-fuel warning inaccurate.
Common causes
Most likely first.
- Bus wiring open or shorted
- Module without power or ground
- Module failed
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
How to diagnose it
- Scan all modules for communication codes and save freeze-frame data, checking whether the problem is limited to sensor B or appears alongside broader network faults.
- Check live data for fuel level sensor B and compare it with the gauge and the known fuel level; a missing or frozen B reading helps localize the fault.
- Inspect sensor B's connector and accessible wiring for loose pins, corrosion, chafing, or damage near the tank.
- Measure sensor B's power and ground against the manufacturer's specification.
- Test the network circuit serving sensor B for opens or shorts using the manufacturer's procedure.
- If wiring and supplies pass, follow the manufacturer's diagnostic steps to confirm a failed sensor B or its communication module.
Common fixes
- Reconnect or clean sensor B's connector and repair damaged wiring.
- Repair a faulty power or ground connection to sensor B or its module.
- Repair an open or short in sensor B's network wiring.
- Replace the confirmed failed fuel level sensor B or communication module.
Can I keep driving?
If the vehicle runs normally, driving is generally possible, but the gauge and low-fuel warning may not reflect the actual fuel remaining; refuel early and monitor mileage. Do not assume a normal gauge reading means the tank has fuel.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.