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U0668 — Lost Communication Engine Oil Level Sensor Circuit

Generic OBD-II · all makesNetwork / communication

Code U0668 indicates a loss of communication between the vehicle's main control module and the engine oil level sensor module on the data bus. This prevents the vehicle from monitoring oil levels accurately and may trigger warning lights or disable certain engine management strategies. The issue typically stems from electrical faults within the sensor circuit rather than a failure of the engine computer itself.

Symptoms

What causes it — most likely first

1. Failed oil level sensor module

The internal electronics of the oil level sensor often fail due to exposure to heat, vibration, or oil contamination, causing it to stop transmitting data.

2. Open or shorted wiring harness

Wires connecting the sensor to the data bus can become damaged, corroded, or disconnected, interrupting the communication signal.

3. Poor electrical connections

Corrosion, bent pins, or loose fits at the sensor connector or ground points can prevent reliable data transmission.

4. Blown fuse or power supply issue

If the sensor module lacks power due to a blown fuse or faulty relay, it cannot communicate on the network.

5. Data bus network fault

Shorts or high resistance on the shared communication bus (CAN or LIN) caused by other components can disrupt messages from the oil sensor.

6. Faulty control module (PCM/ECM)

While possible, internal failure of the main computer preventing it from reading the bus is statistically rare compared to sensor or wiring faults.

How it's diagnosed

  1. Verify the code with a scan tool and check for related communication codes in other modules.
  2. Inspect the oil level sensor connector and wiring for visible damage, corrosion, or disconnection.
  3. Test power and ground circuits at the oil level sensor connector using a multimeter.
  4. Measure resistance and continuity of the data bus wires between the sensor and the control module.
  5. Swap the oil level sensor with a known good unit if accessible to verify if communication is restored.
  6. Perform network integrity tests to rule out bus-wide communication failures before considering module replacement.

Code facts & related codes

SystemNetwork / communication
StandardizationSAE generic — identical on every make
Related codesU0660 — Lost Communication Left Rear TemperatuU0661 — Lost Communication Right Rear TemperatU0662 — Lost Communication Right Rear TemperatU0663 — Lost Communication Rear Mode ActuatorU0664 — Lost Communication Rear Hvac Air CutofU0665 — Lost Communication Fuel Rail Pressure

Frequently asked

Does code U0668 mean I need to replace the engine computer (PCM)?

No, this code rarely indicates a failed PCM. In the vast majority of cases, the fault lies with the oil level sensor itself, its wiring, or its power supply. Replacing the computer without exhaustive testing of the sensor circuit is usually unnecessary and incorrect.

Can I drive the vehicle with this code?

While the vehicle may run, driving without a functional oil level monitoring system is risky as low oil conditions will not be detected. Immediate inspection is recommended to prevent potential engine damage.

Why did this code appear suddenly?

Sudden appearance often points to a wiring harness chafing against a moving part, a connector vibrating loose, or an immediate internal failure of the sensor electronics due to age or heat stress.

Will resetting the code fix the problem?

Resetting the code will clear the light temporarily, but if the underlying communication loss persists, the code will return immediately or after a few drive cycles.