Oil Temperature Sensor/Switch: Description and Operation

Engine Oil Temp Sensor Circuit:

DESCRIPTION
The engine oil temperature sensor is a thermistor, installed on the front of the engine near the oil filter. Resistance through the sensor changes inversely with changes in temperature. Resistance begins high when the sensor is cold, and decreases as sensor temperature increases.

PURPOSE
The ECM monitors engine oil temperature to help control outputs such as cooling fan operation, secondary port throttle valve system, and shares this information with the CCM for use by the "Oil Life Monitor" system in determining when to notify the driver that an oil change is due.

OPERATION
The ECM applies a 5 volt reference voltage to the sensor through a resistor in the ECM, and then monitors the voltage in the circuit. When the engine oil is cold, resistance through the sensor will be high and the voltage in the circuit will be near the reference voltage of 5V. When the temperature increases, resistance drops, more current flows through the circuit and the voltage in the circuit will drop. Each voltage value corresponds to a specific resistance through the sensor and a specific temperature. The ECM measures this voltage and calculates the engine oil temperature.