What does it mean?
This code means the signal voltage on the engine oil temperature sensor B circuit has fallen below the module minimum. With the usual thermistor and internal pull-up arrangement, the sensor pulls the line closer to ground as the oil gets hotter, so a signal at or near zero volts corresponds to an oil temperature the engine could never reach.
The module tests the value against a fixed low threshold and stores the code when the condition persists, then substitutes a default oil temperature for the strategies that need one. A short to ground in the signal wire or an internally shorted sensor is the usual cause, and both are far more likely than genuinely overheated oil.
Since a falsely hot reading can also lead the module to change how it manages valve timing or thermal protection, the fault should not be ignored simply because the engine seems to run normally.
Symptoms
- MIL (check engine lamp) on with an oil temperature fault stored
- Oil temperature reading at the very top of the scale even on a cold engine
- Oil temperature warning message or lamp on vehicles that display one
- Cooling fans running earlier or harder than expected
- Variable valve timing behaving as though the oil were fully hot from the moment of starting
- Occasional reduced power depending on how the strategy uses the value
Likely causes
- Signal wire shorted to ground, often where the harness rubs the block, a bracket or the exhaust shield
- Oil contamination or corrosion inside the sensor connector bridging the signal to ground
- Thermistor shorted internally, showing almost no resistance
- Melted harness insulation from contact with the exhaust or turbocharger
- Signal wire pinched or trapped during a previous engine repair
- Incorrect sensor fitted with a much lower resistance curve
- Engine control module input circuit failure, the least likely cause
How to fix it
- Read live oil temperature B on a cold engine; a value at maximum with a cold block confirms an electrical fault
- Disconnect the sensor and watch the scan tool. A swing to minimum temperature shows the harness is good and the sensor is shorted internally
- If the value stays at maximum with the sensor unplugged, the signal wire is shorted to ground and must be traced
- Measure the sensor resistance and compare it with the specification for the current temperature
- Inspect the harness along the block and near the exhaust for melted, chafed or trapped insulation
- Repair the shorted conductor, re-route and protect the loom, then clear the code and verify the reading tracks warm up correctly
- Replace oil temperature sensor B when the wiring measures good and the sensor resistance is near zero