Theory Of Operation

The Engine Oil Temperature (EOT) Sensor is incorporated into the Engine Oil Pressure (EOP) Sensor.  The EOP Sensor provides both a pressure and temperature signal feedback to the Powertrain Control Module (PCM). The sensors share the common sensor ground circuit but the 5-Volt supply circuit is only used for the internal pressure sensor.

The EOT Sensor is a variable resistor that operates as a typical two wire sensor. The Powertrain Control Module (PCM) supplies the sensor with a 5-Volt signal and the shared sensor ground circuit. For the EOT Sensor diagnostic, the PCM internally monitors the voltage on the signal circuit, which is converted into a temperature reading. When the oil temperature is low, the sensor resistance is high. When the oil temperature is high, the sensor resistance is low.

Rationality Diagnostics:  Once the Ambient Air temperature (AAT), Intake Air Temperature (IAT), and Engine Coolant Temperature (ECT) Sensors have been evaluated the Engine Oil Temperature (EOT) Sensor can be checked. If the ambient, engine coolant, and general temperature sensor rationalities indicate valid sensor readings then the engine oil temperature rationality will assume the AAT and ECT Sensors are correct and therefore can be used to evaluate the EOT Sensor.

To determine failing status, the difference between the starting EOT and starting ECT is compared to a threshold. If the calculated difference is above the threshold, then starting EOT is compared to starting AAT. The diagnostic will check if a block heater is being used to determine if larger threshold values are needed. If this rationality test fails, then it is tested again using the updated value of AAT. A failure here will result in a fault being set for EOT sensor rationality.