Theory Of Operation

The purpose of the diagnostic is to detect rationality failures of the transmission oil temperature sensor by evaluating the following conditions:

Comparison to a Temperature Model

• The measured transmission oil temperature is compared to a calculated model temperature. The calculation of the modeled temperature is based on the fact that the resistance of the pressure regulator coil is correlated with the oil temperature. The calculation is based on the actual duty cycle of pressure regulator for a given commanded current and the value of the pressure regulator power supply.

Low Temperature Detection

• The measured transmission oil temperature is monitored for a low value after having first reached a fixed temperature value.

Stuck in Low Temperature Detection

• The measured transmission oil temperature is monitored for a minimum amount of temperature change at low temperatures.

Temperature Jump Detection

• The measured transmission oil temperature is monitored for a maximum amount of temperature change between two consecutive data samples.