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U0670 Lost Communication With Fuel Temperature Sensor A

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modeNo

GM's 2025 direct-injection engines measure fuel temperature in the high-pressure rail with digital SENT sensors, and sensor 1 is the one GM files under U0670. The test counts pulses on the signal wire: if the line sits permanently high and four or fewer pulses arrive (25OBDG03A; 40 or fewer in 25OBDG03B), a sample fails, and 400 bad samples in a window of 500, one every 6.25 ms, set the code; being Type A, it lights the MIL during the first trip. While it is active, GM holds back the range checks P0182/P0183 and the sensor comparison P111F. CARB requires a separate code when a digital input stops talking. The controller then substitutes a fuel temperature, so drivability rarely changes; the fault lies in wiring, connector or sensor.

Likely causes

SENT signal wire to sensor A shorted or open

Connector at the fuel rail loose or contaminated

Fuel temperature sensor A internally failed

SENT receiver in the engine controller faulty

Symptoms

Check engine light from the first trip
Usually no noticeable change in driving
Occasionally rougher hot restarts

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€60–400

Time0.5–2 h

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

Parts involved

fuel temp sensor avehicle bus wiring

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