Transmission fluid temperature sensor: Notes
The fluid temperature sensor, which is fitted in the transmission casing, supplies the control module with information on the current fluid temperature.
The sensor is NTC type, i.e. the integral sensor resistance is inversely dependent on the temperature. This means that the resistance decreases as the temperature increases.
Through an integral 1 kohm resistor, the transmission control module measures the temperature of the transmission fluid by applying +5 V to the sensor from pin 6.
The sensor is grounded at grounding point G34S.
In all variants, the control module uses temperature information for the following:
- For calculating when to shift and when to engage the lock-up function.
- At fluid temperatures below 0°C lock-up is not engaged
- At fluid temperatures below 0°C, the system pressure is raised by 3.3 bar for 5 seconds when shifting from N to D or N to R. At fluid temperatures between 0 and 20°C, the same function is implemented but the pressure increase is reduced linearly from 3.3 bar at 0°C to 0 bar at 20°C.
In T7 with bus, the control module uses temperature information for the following:
- At fluid temperatures of about 170°C, the TCM sends "HIGH TRANSMISSION FLUID TEMPERATURE ON" over the bus, and the corresponding message is then shown on the SID. When the fluid temperature has lowered and is below 140°C, "HIGH TRANSMISSION FLUID TEMPERATURE OFF" is sent over the bus, at which the SID message is extinguished and the function of the transmission returns to normal.