Transmission fluid temperature sensor
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Transmission fluid temperature sensor
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The oil temperature sensor mounted on the valve housing gives the control module information on the current oil temperature. The sensor is a NTC-type (Negative Temperature Coefficient).
The control module measures the temperature of the gearbox oil by supplying the sensor with +5 V through a 1 kOhm resistor integrated into the control module, and out via pin 21 (B). When the temperature of the oil rises the resistance in the NTC resistor decreases. This means that the flow increases and causes a voltage drop across the NTC resistor measured by TCM.
The sensor is grounded in pin 31 (B).
The control module uses the oil temperature for the following purposes:
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Control engagement and disengagement of lock-up. There will be no lock-up at temperatures below 20°C and no lock-up slip at temperatures under 40°C.
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To control the different temperature programs.
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To warn the driver of overheated transmission.
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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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Oil temperature °C
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Resistance Ω ±10%
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Voltage (TCM) V ±10%
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-10
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5000
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4.6
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0
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2000
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4.1
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20
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900
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3.4
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40
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400
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2.4
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80
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125
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1.1
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100
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75
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0.7
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150
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27
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0,3
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If the oil temperature rises to 128°C lock-up is activated on 3rd and 4th gear. With lock-up activated there is no slip in the torque converter, which means that temperature falls. The shifting points are also changed so that changing up takes place at higher engine speeds and changing down at lower engine speeds than in the normal program.
Temperature program 1 does not function when:
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Winter program is selected
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Is disengaged when:
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The temperature has fallen to 120°C
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If the oil temperature rises to 135°C lock-up is activated on 2nd gear. This can take place for example on a hill with a caravan attached. With lock-up activated there is no slip in the torque converter, which means that temperature falls.
Temperature program 2 does not function when:
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Winter program is selected
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Is disengaged when:
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The temperature has fallen to 130°C
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If the temperature rises to 145°C a reduction of engine torque to 200 Nm takes place.
Temperature program 3 is disengaged when:
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WINTER mode is selected
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The Limp Home mode has been entered
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The temperature has fallen to 135°C
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If the temperature rises to above 155°C for more than 10 seconds or 140°C for more than 60 seconds at speeds above 180 km/h then diagnostic trouble code P0218 is registered. A bus message “TRANSMISSON OVERHEATING”, is sent from TCM, this is shown in the SID display and the transmission goes into Limp Home. (Only 5th, 2nd and reverse gear are then available.)
