Theory Of Operation

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 to see 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.