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DTC codes / U06xx · Network communication / U0668

U0668Lost Communication With Engine Oil Level Sensor Circuit

U0668 is a generic network communication code indicating that a control module on the vehicle's Controller Area Network (CAN) bus has stopped receiving valid messages from the engine oil level sensor circuit. The module that sets this code, typically the engine control module or a body control module, expected regular status updates from the oil level sensor but detected a loss of communication, which can be caused by wiring faults, connector issues, or a failed sensor.

SystemNetwork
Code typeGeneric (all makes)
SeverityLow
Fix difficultyIntermediate
AreaNetwork communication

Symptoms you may notice

  • Illumination of the check engine light or a dedicated oil level warning light on the dashboard
  • Often no symptoms besides the warning light, especially if the oil level is actually correct
  • Inaccurate or missing oil level display on vehicles equipped with an electronic oil level gauge
  • A generic communication fault code stored in one or more modules, sometimes with other U-codes
  • In rare cases, the engine may enter a reduced power or default mode if the module relies on oil level data for protection strategies

Common causes, most likely first

  1. Failed engine oil level sensor or sending unit
  2. Damaged, corroded, or disconnected electrical connector at the oil level sensor
  3. Open or shorted wire in the sensor signal or ground circuit
  4. Faulty CAN bus communication line between the sensor and the control module
  5. Low system voltage or a weak battery causing intermittent communication dropouts
  6. Water or oil intrusion into the sensor connector or wiring harness
  7. Internal fault in the control module that monitors the oil level sensor circuit

How to diagnose and fix it

  1. Verify battery voltage and charging system health, as low voltage can cause false communication codes
  2. Inspect the oil level sensor connector and wiring for corrosion, looseness, or damage, and clean or repair as needed
  3. Check the sensor ground circuit for continuity and proper resistance to ground
  4. Measure the signal voltage or resistance from the oil level sensor according to the manufacturer's specification
  5. Clear the code and test-drive the vehicle to see if it returns, monitoring live data for oil level sensor communication
  6. If the sensor fails specification, replace the engine oil level sensor and clear the code
  7. If wiring and sensor are good, diagnose the CAN bus circuit or the control module itself using a scan tool and oscilloscope

Oil Level Sensor Communication Traps

  • A loose or corroded connector at the oil level sensor is a far more common cause of U0668 than a failed sensor, so always inspect the plug before condemning the part.
  • This code can set intermittently due to a weak battery or poor ground connection, and it may not return after clearing if the underlying voltage issue is resolved.
  • Some vehicles use the oil level sensor data for oil change interval calculation, so a communication fault can trigger a service reminder even when the oil itself is fine.
  • U0668 is often stored alongside other U-codes if the CAN bus is disrupted, so diagnosing the root network fault may resolve multiple codes at once.
  • Do not replace the control module before verifying the sensor and wiring, as module replacement requires programming and is rarely the actual fix for this code.

Can I keep driving with U0668?

It is generally safe to continue driving with U0668 because the engine oil level sensor is not critical for engine operation, but you should check the oil level manually with the dipstick and address the fault soon to avoid missing a genuine low-oil condition.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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