3.9 Transmission Fluid Temperature Sensor
3.9 Transmission Fluid Temperature Sensor3.9.1 Description
The transmission fluid temperature (TFT) sensor is a positive temperature coefficient sensor, containing semiconductor material, which increases its resistance as the temperature increases.
The sensor receives a predetermined current from the TCM on one of the wires and is connected to earth via the TCM on the second wire. The TCM measures the returned voltage and using this information calculates the TFT.
In the case of low fluid temperatures, the TCM prohibits torque converter clutch lock-up to promote faster fluid warm up. In the case of high fluid temperatures, the TCM increases the converter lock-up control and modifies the shift program to reduce fluid temperature.
If the sensor fails, the TCM uses a programmed default temperature value. The default value is derived from the ECT sensor and received on the CAN from the ECM.
There are seven diagnostic checks for the TFT sensor, an error is detected if:
1. The voltage at the positive connection to the sensor is greater than 4.5V and the voltage at the negative connection of the sensor is less than 0.5V. This indicates an open circuit condition.
2. The voltage at the positive connection of the sensor is greater than 4.5V and the voltage at the negative connection of the sensor is greater than 0.5V. This indicates a short to battery voltage condition.
3. The voltage at the positive connection to the sensor is less than 4.5V and the voltage at the negative connection of the sensor is less than 0.5V. This indicates a short to ground condition.
4. The voltage at the positive connection of the sensor is greater than 2.3V and less than 2.7V and the voltage at the negative connection of the sensor is greater than 2.3V and less than 2.7V. This indicates a short circuit across the sensor.
5. The temperature rise between readings is greater than 20 OC.
6. The temperature rise since engine start is less than 4 OC.
7. The temperature value has not changed by more than an acceptable value when compared to the TCM chip temperature sensor.
If the above table does not include details of the following enabling conditions: - IAT, ECT, vehicle speed range, and time after engine start-up then the state of these parameters has no influence upon the execution of the monitor.
1) The voltage on the positive connection to the sensor is between 2.3 and 2.7 volts and the voltage on the negative connection to the sensor is between 2.3 and 2.7 volts.
*2) utmso_Gt = voltage at positive connection to sensor utmsu_Gt = voltage at negative connection to sensor In this instance, these are both low limits.
*3) utmso_Gt = voltage at positive connection to sensor utmsu_Gt = voltage at negative connection to sensor In this instance, these are both high limits.
*4) utmso_Gt = voltage at positive connection to sensor utmsu_Gt = voltage at negative connection to sensor In this instance, utmso_Gt is a low limit and utmsu_Gt is a high limit.