What does it mean?
Engines that report both coolant temperature and engine oil temperature give the module two independent views of how hot the engine is. After a long stand the oil in the sump, the coolant in the block and the surrounding air all settle at the same temperature, so the module compares the two sensors at the first key on and expects them to agree closely. This code is stored when the difference exceeds the calibrated window, which means one of the two readings is wrong even though both circuits are electrically normal. Oil temperature also feeds service interval calculation and protection strategies, so a drifted value has effects beyond the code itself.
Symptoms
- MIL on, generally noticed at the first start after the vehicle has stood
- Temperature gauge and any oil temperature display that disagree with each other
- Cooling fan or thermostat control behaving differently from normal
- Service interval or oil condition calculation that no longer matches how the vehicle is used
- Slightly rough cold running and higher fuel consumption
- Protective strategies on some vehicles reducing power when the module believes the oil is too hot
Likely causes
- Engine oil temperature sensor drifted, or its tip coated with sludge so it responds slowly and reads incorrectly
- Coolant temperature sensor drifted without leaving its electrical range
- Low oil level leaving the oil temperature sensor tip out of the liquid
- Low coolant level or an air pocket at the coolant sensor
- High resistance in the signal or ground circuit of either sensor
- Incorrect replacement sensor with a different resistance curve
- Corroded terminal or a damaged pin at one of the module inputs
How to fix it
- After a full cold soak, read both temperatures with the key on before starting and compare them with a measured ambient temperature
- Cross check with an infrared thermometer on the sump and on the thermostat housing while everything is still cold
- Verify oil level and coolant level, since a sensor tip surrounded by air or foam cannot read correctly
- Measure each sensor resistance or signal voltage against its temperature specification
- Check both circuits for voltage drop on the ground and reference sides and inspect the connectors
- Consider sludge or contamination in the oil, which slows the oil sensor and points to a wider maintenance issue
- Replace the sensor proven to be wrong with the correct part, then repeat the cold soak comparison