U0668 — Lost Communication With Engine Oil Level Sensor Circuit

Causes

• Open or shorted wiring between the oil level sensor and control module
• Corroded or loose connector at the sensor or control module
• Failed oil level sensor (internal electronics or transceiver)
• Faulty power or ground to the sensor
• Fault, loss or bus error on the vehicle communication network (LIN/CAN)
• Blown fuse or module power supply issue

Symptoms

• Malfunction Indicator Lamp (MIL) or warning message for oil level or service required
• Instrument cluster shows no oil level, intermittently updates, or displays error
• Oil level readout stuck at one value or shows implausible values
• Possible reduced drivability if the vehicle goes into limp mode (rare)
• Related communication DTCs present on the network

What to check

• Connect a quality scan tool; read U0668 and any other stored/active network DTCs and freeze frame data
• Confirm whether oil level data is present on the network data list (live data) or missing
• Visually inspect sensor connector and harness for damage, corrosion, chafing, or oil contamination
• Check fuses and module power/ground circuits related to the sensor
• Backprobe sensor connector to verify supply voltage and ground with key ON
• Use a scope or data logger to view the bus (LIN or CAN) signals while cranking/operating

Signal parameters

• Sensor supply: typically 5 V or 12 V depending on vehicle (verify service manual)
• Ground: near 0 V (less than 0.2 V drop under load)
• LIN bus: single-wire ~12 V idle, dominant low pulses to ~0 V (if oil sensor uses LIN)
• CAN bus (if used): recessive ~2.5 V on CAN_H and CAN_L, dominant ~CAN_H ≈3.5–4.0 V and CAN_L ≈1.0–1.5 V
• Expected message frequency: usually periodic (0.5–5 Hz) or on-change; check vehicle-specific data list
• Sensor current draw: typically low (tens of mA); large increases indicate internal fault

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