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U0671 Lost Communication With Fuel Temperature Sensor B

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modeNo

Sensor B is the second SENT temperature sensor in GM's high-pressure fuel rail (sensor 2 in 25OBDG03A and 25OBDG03B). Its link test mirrors that of sensor A, line stuck high with too few pulses, 400 of 500 samples at 6.25 ms, Type A. What sets B apart is its job: GM compares it with sensor 1 and stores P111F when the two differ by more than 10 °C in 100 of 125 samples, and it checks the raw digital value of sensor 2 against limits below 145 and above 1,865 counts (P0187/P0188, Type B). Without B both checks go blind, so a drifting sensor A could go unnoticed. If U0670 and U0671 appear together, look first at a shared connector, supply or ground; if only B is missing, its own branch or sensor is more likely.

Likely causes

Signal wire of sensor B chafed, shorted or open

Shared 5 V supply or ground of both rail sensors faulty

Fuel temperature sensor B defective

Engine controller input or software fault

Symptoms

Check engine light
Sensor comparison and range checks of sensor B not completed
Often no drivability complaint

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 bvehicle bus wiring

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