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Transmission fluid temperature sensor

Transmission fluid temperature sensor

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.

The control module uses temperature information on all variants for the following:

-To calculate shifting points and engage Lock-Up.

-Lock-Up is not activated when the fluid temperature is below 0°C

- The system pressure is increased by 3.3 bar for 5 seconds when shifting N-D or N-R if the fluid temperature is below 0°C. The same function is implemented when the fluid temperature is between 0-20°C but the rise in pressure is reduced linearly from 3.3 bar (at 0°C) to 0 bar (at 20°C).

In T7 with bus, the control module uses the temperature information for the following:

-At a fluid temperature of approx. 170°C, the TCM sends the buss information “HIGH TRANSMISSION FLUID TEMP ON” and the corresponding message is then displayed on the SID. When the oil temperature has decreased and is less than 140°C “HIGH TRANSMISSION FLUID TEMP OFF” is sent over the bus, at which the SID message is extinguished and the transmission function returns to normal.



Diagnostics

A fault in the temperature sensor can generate the following 3 diagnostic trouble codes:


• If the temperature increases or decreases too slowly during the first 15 minutes of driving, diagnostic trouble code P0711 will be generated.

• A short circuit to B- will generate diagnostic trouble code P0712.

• A break/short circuit to B+ or a break will generate diagnostic trouble code P0713.


Temperature program 1

If the gearbox fluid temperature rises to 130°C, Lock-Up will be engaged in 3rd and 4th gear. Engaging Lock-Up prevents slip in the torque converter, which makes the temperature drop. The shifting points are also changed so that upshifting takes place at a higher engine speed and downshifting at a lower engine speed than when using the normal program. Temperature program 1 does not work when:


• WINTER program is selected

• Limp-home is active

Disengaged when:

• temperature has decreased to 115 degrees


Temperature program 2

If the transmission fluid temperature rises to 145°C, Lock-up will be activated in 2nd gear. This may happen, for example, when driving uphill towing a caravan. Activating Lock-up prevents slip in the torque converter, which makes the temperature drop. Temperature program 2 will not work when:


• WINTER program is selected

• Limp-home is active

Disengaged when:

• temperature has decrease to 135 degrees


Temperature program 3

If the temperature rises to 150°C, the engine torque is reduced to 200 Nm. Temperature program 3 is disengaged when:


• temperature has decreased to 140 degrees and stable for 5 seconds

If these programs do not alleviate the problem and the temperature rises to 170 degrees, the "Info display" lamp lights up and the message TRANSMISSION OVERHEATING is displayed on the SID. Diagnostic trouble code P0218 can be read with Tech 2. If this trouble code is displayed, the transmission fluid must be changed.