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U0668 Lost Communication With Engine Oil Level Sensor Circuit

Check engine lightUsually off

EmissionsNot relevant

Drive cycleNot required

Limp modeNo

Despite the word circuit in its name, U0668 concerns the data link to the oil level sensor, not a voltage fault. Sensors in the sump measure the oil height either thermally or by ultrasound; Hella's PULS type packs an ultrasonic transducer, a temperature sensor and an ASIC into one module that sends its result to the engine controller over a single signal line, and loss of supply or ground is one listed failure cause. When that signal no longer arrives or is unreadable, a separate lost-communication code can be stored. No manufacturer documents U0668 in public. Because oil level is normally not emission-relevant, CARB's rule on separate codes for silent digital inputs hardly applies. Electrical sensor faults are P250A to P250E, low or high oil P250F and P252F. Check the dipstick until fixed.

Likely causes

Missing supply voltage or ground at the sensor

Sensor electronics failed or oil inside the housing

Corroded or damaged connector or harness at the oil pan

Receiving control unit input faulty

Symptoms

Oil level warning or service message in the display
Oil level reading unavailable

Repair estimate

DifficultyEasyDIY possible

Parts and labour€40–400

Time0.3–2 h

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

Parts involved

engine oil level sensorvehicle bus wiring

References: hella.com, law.cornell.edu.