Theory Of Operation

The purpose of the diagnostic is to check the torque converter fluid temperature sensor for rationality failures by performing three separate checks. These checks include stuck in range, maximum gradient, and three sensor compare. This fluid temperature sensor (thermistor), which correlates resistance to temperature, measures the temperature of the fluid coming out from torque converter. Temperature values are calculated by the TCM based on the sensor's voltage output for shift map determination and sump fluid temperature rationality checks.

• Stuck in Range:  If the absolute value of the change in torque converter fluid temperature is less than or equal to a calibrated threshold for a calibrated amount of time when compared to the actual increase of engine coolant temperature, a DTC will be set.
• Maximum Gradient:  If the absolute value of the change in torque converter fluid temperature is greater than or equal to a calibrated threshold for a calibrated amount of time, a DTC will be set.
• Three Sensor Compare:  If the torque converter fluid temperature is greater than or equal to a calibrated threshold while the Transmission sump fluid temperature is less than or equal to its calibrated threshold for a calibrated amount of time, a DTC will be set.