Network, generic

U0678 Lost Communication With Fuel Level Sensor C

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modeNo

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.

Likely causes

Wiring to sender C damaged or corroded

Sender C electronics failed

Module receiving the level data faulty

Symptoms

Gauge or range wrong when the third chamber is involved
Check engine light
EVAP readiness not completed

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€60–650

Time0.5–3.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

fuel level sensor cvehicle bus wiring

References: law.cornell.edu, fordservicecontent.com, gsi.ext.gm.com.