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U0677 Lost Communication With Fuel Level Sensor B

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modeNo

A second level sender is needed when a tank has two chambers, as in saddle tanks that straddle the driveshaft, or when a vehicle carries a second tank. GM's 25OBDG03B calls it sensor 2 of the secondary tank, used on vehicles with two senders and a mechanical transfer pump; its circuit checks fail below 10 % or above 60 % of the 5 V range in 40 of 50 samples (P2067/P2068, Type B). Ford's 2024 summary runs sender B through the same resistance, noise and stuck checks as A and adds P25B2 for a stuck reading on either. U0677 is the digital variant: sender B's messages stop arriving. No manufacturer documents it publicly. The gauge then misjudges the part of the tank sender B covers, and range and EVAP readiness suffer.

Likely causes

Wiring to the secondary-chamber sender damaged

Sender B electronics failed

Connector at the secondary flange corroded

Receiving module or software faulty

Symptoms

Gauge drops suddenly or never shows full
Range estimate inaccurate
Check engine light

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 bvehicle bus wiring

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