U0678 code meaning
Lost Communication With Fuel Level Sensor C
Network system Generic code U06xx codes Check engine light
What U0678 means
A third level sender only makes sense where the fuel volume is split further, for example a tank with three chambers or a main tank plus an auxiliary one. U0678 would be stored when such a sender C reports its value as a message and that message is lost. No manufacturer documents U0678 publicly, and the public OBD summaries checked here stop at two senders: GM's 2025 tables and Ford's 2024 summary, which covers A and B and a combined stuck code P25B2. The analog counterparts for C exist as P25D7 to P25DC. CARB lists stuck fuel level sensors among inputs that need extended monitoring, and the level enables EVAP tests, so a missing third reading keeps those monitors from running and leaves the gauge inaccurate.
U0678 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0678
- Gauge or range wrong when the third chamber is involved
- Check engine light
- EVAP readiness not completed
Common causes of U0678
- Most likelyWiring to sender C damaged or corroded
- PossibleSender C electronics failed
- Less likelyModule receiving the level data faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Fuel level sensor cVehicle bus wiring
What each part of U0678 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 78 | The exact fault in that area. |
What to do next
- Note U0678 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 U0678
What does U0678 mean?
U0678 means "Lost Communication With Fuel Level Sensor C". A third level sender only makes sense where the fuel volume is split further, for example a tank with three chambers or a main tank plus an auxiliary one. It is a generic code, so it means the same on every make.
Is it safe to drive with U0678?
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 U0678 fail an emissions test?
Yes, it can. U0678 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 U0678 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3.5 hours of work. This is a job for a workshop.
Will U0678 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.