What does it mean?
Here the engine oil temperature sensor B signal is sitting at or above the module upper voltage limit. With the module pulling the input up through an internal resistor, any open in the signal wire, the sensor ground or the thermistor itself will leave the line near reference voltage, and the strategy converts that into an implausibly cold oil temperature.
The module cross-checks against coolant and intake air temperature and against the ends of the thermistor curve, then stores the code once the signal has exceeded the threshold for the calibrated time. Because the engine control module then assumes cold, thick oil, it can delay or limit hydraulic functions such as variable valve timing and may extend warm-up enrichment. Broken connections are far more common than an oil temperature that is genuinely below the sensor range.
Symptoms
- MIL (check engine lamp) on with an oil temperature fault stored
- Oil temperature reading at the bottom of the scale even after a long drive
- Sluggish variable valve timing response and a slight loss of low-end torque
- Extended warm-up enrichment with higher fuel consumption
- Oil life or service interval calculation not progressing correctly
- Cooling fan or thermal management behaviour that seems out of step with the engine load
Likely causes
- Open circuit in the signal wire or in the sensor ground return
- Connector unplugged, unlatched or with a corroded, backed-out terminal
- Thermistor failed open internally
- Harness broken inside its insulation after long term heat cycling on the engine
- Signal wire shorted to a reference or battery voltage from an adjacent circuit
- Sensor damaged or its connector disturbed during a previous oil service
- Engine control module input circuit failure, the least likely cause
How to fix it
- Read live oil temperature B on a fully warmed engine and compare it with coolant temperature; a value far below coolant confirms the complaint
- With the ignition on and the sensor unplugged, jumper the signal pin to ground at the harness connector. A reading that swings to maximum temperature proves the wiring and module are good
- If the reading stays at minimum with the pin grounded, trace the signal wire and the ground path for an open
- Inspect the connector for corroded, spread or backed-out terminals and a broken locking tab
- Measure the sensor resistance; an infinite reading confirms an open thermistor
- Repair the open wire, terminal or ground and protect the repair from engine heat, then clear the code and verify the reading climbs during warm up
- Replace oil temperature sensor B when the harness has tested good and the element reads open