Transmission fluid temperature sensor
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Transmission fluid temperature sensor
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The transmission fluid temperature sensor is mounted in the gearcase and provides the control module with information on the current transmission fluid temperature. The sensor is of NTC type.
The control module senses the transmission fluid temperature by supplying the sensor with +5 V current through a 1 kohm resistor (built into the control module) and out on pin 6.
The sensor is grounded at grounding point G41S.
The control module uses the fluid temperature for the following purposes:
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At fluid temperatures below 0°C, no Lock-up takes place.
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At a fluid temperature of approx. 170°C, the TCM sends the bus information “HIGH TRANSMISSION FLUID TEMP ON” and the corresponding message is then displayed on the SID.
When the fluid temperature drops to below 140°C, the information “HIGH FLUID TEMP AUT TRANSMISSION OFF” is sent on the bus. The SID message then goes out and operation of the transmission returns to normal.
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At fluid temperatures below 0°C, system pressure is increased by 3.3 bar for 5 seconds when N-D or N-R shifts are performed.
At fluid temperatures 0-20°C the same function is implemented but the increase in pressure is reduced linearly from 3.3 bar (at 0°C) to 0 bar (at 20°C).
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The transmission fluid temperature is above 150 °C.
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Diagnostics
In the event of a fault in the temperature sensor, three different diagnostic trouble codes may be generated:
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If the temperature increases or decreases too slowly during the first 15 minutes of driving, diagnostic trouble code P0711 will be generated.
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In the event of short to B-, diagnostic trouble code P0712 will be generated.
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In the event of short to B+ or an open circuit, diagnostic trouble code P0713 will be generated.
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If the oil temperature rises to 125° C, Lock-up will be activated in the 3rd and 4th gear. When lock up is activated no slipping will occur in the torque converter, which results in a lower temperature. The shifting points are altered as well which means upshifts occur at higher engine speeds and downshifts at lower engine speeds. Temperature program 1 does not function when:
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Winter program is selected
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Limp home has been activated
Is disconnected when:
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The temperature drops to 110°C
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If the oil temperature rises to 140°C, Lock-up will be activated in 2nd gear. This can occur, for example, when driving on uphill stretches with a caravan attached. When lock-up is activated no slipping occurs in the torque converter, which results in a lower temperature. Temperature program 2 does not work when:
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Winter program is selected
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Limp home has been activated
Is disconnected when:
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The temperature drops to 125°C:
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If the temperature rises to 150°C, a reduction of the engine torque to 200Nm will take place. Temperature program 3 is deselected when:
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The temperature drops to 140°C
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If these programs do not alleviate the problem and the temperature rises to 170°C, 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.
