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.

The EOP Sensor is a variable resistor that operates as a typical three wire sensor. The PCM provides a 5-Volt supply to the EOP Sensor on the 5-Volt supply and the shared sensor ground. The Engine Oil Pressure Sensor signal can be a pull up (5.0 volts) or pull down (0.0 volts) resistor depending on the PCM internal hardware for the signal circuit. This can vary between vehicles and model years. The PCM manages the information received by the EOP sensor with specific strategies that may lead to an Instrument Cluster oil lamp switched ON in particular conditions. The strategy is based on the expected pressure based on engine working condition and oil temperature of the oil prescribed in the service information. This strategy includes a buffer in cold conditions or at key on to prevent misdiagnosis. This strategy keeps the oil lamp switched ON for the entire driving cycle in when the oil pressure is detected below the calibrated threshold, even if the oil pressure is returns to normal. The lamp is re-initialized (switched off) in the following driving cycle.