Four Wheel Drive Selector Switch: Description and Operation

Description

The TCM uses this sensor to monitor the gearbox fluid temperature. When the fluid is cold, the TCM changes gear at higher engine speeds to promote faster fluid warm-up. If the fluid temperature becomes too high, the TCM transmits a cooling request on the CAN link to the ECM to operate the cooling fans.

The fluid temperature sensor is a negative temperature coefficient sensor. As the temperature rises, the resistance in the sensor decreases. As temperature decreases, the resistance in the sensor increases and the output voltage to the TCM changes in proportion. The output voltage from the sensor is in the range of 0 - 2.5 Volts with the lower voltage representing the highest temperature. The change in resistance is proportional to the temperature of the gearbox fluid. From the resistance of the sensor, the TCM calculates the temperature of the gearbox fluid. Should the fluid temperature sensor fail the TCM uses ECM engine coolant temperature; if the engine coolant temperature fails a fixed value is used.

The diagnostic changed between 2002MY and 2003MY. At 2002MY a fault was identified if the sensor exceeded the minimum or maximum threshold value identified in the table below for a time of 180 s. At 2003MY and beyond a fault is identified if the sensor remained within the threshold values identified in the table for the given period.