Gearbox oil temperature sensor

Gearbox oil temperature sensor

For optimal shift characteristics, the EGS control unit requires the input signal from the gearbox temperature sensor. At very low gearbox oil temperatures, the shifting forces to be applied are high; at operating temperature, they are correspondingly low. The gearbox temperature sensor is installed in the mechatronics module. Activation of the converter lockup clutch, among other things, is controlled according to the gearbox oil temperature.

Brief description of components

The gearbox temperature sensor is a thermistor where the output value changes according to the gearbox oil temperature. The sensor has negative temperature coefficient. With rising temperature, the resistance falls and with falling temperature the resistance increases. The EGS control unit sends a reference signal to the sensor and measures the voltage drop in the circuit. At low gearbox oil temperature, the sensor resistance is high and the EGS control unit picks up a high signal voltage. When the gearbox oil temperature rises, the resistance becomes lower and the signal voltage drops.

System functions

The following system function is described:

Closing the converter lockup clutch

Below the following gearbox oil temperature, the converter lockup clutch is not regulated or closed.

• N51 engine: 7 °C
  
• N45, N46, N52 engines: 17 °C
  
  

Opening the thermostat in the gearbox oil cooler

The automatic gearbox oil is cooled in the cooling circuit. A thermostat is installed in the gearbox oil cooler. The thermostat is opened or closed on a temperature-dependent basis.

• E81, E87, E90, E91, E92, E93
  The thermostat regulates coolant volume that flows through the gearbox oil cooler depending on the gearbox oil temperature.
  The thermostat opens above a gearbox oil temperature of 92 °C
  

• E83
  The thermostat regulates coolant volume that flows through the gearbox oil cooler depending on the coolant temperature.
  The thermostat opens above a coolant temperature of 75 °C
  
  

Notes for Service department

General information

The gearbox temperature sensor can not be replaced separately.

Diagnosis instructions

Relevant faults for the sensor system

The following faults are treated in the test module:

• 5781 gearbox temperature sensor: implausible
  5782 gearbox temperature sensor: value too low
  5783 gearbox temperature sensor: value too high
  5785 internal temperature sensor: Power output
  5786 internal temperature sensor: value too low
  5787 internal temperature sensor: value too high
  5788 hot cutout
  578A increased gearbox temperature
  578B gearbox temperature sensor: plausibility
  578C internal temperature sensor: plausibility
  578D internal temperature sensor: plausibility
  5780 excess temperature gear oil
  

The internal temperature sensor is integrated in the EGS control unit.

No liability can be accepted for printing or other errors. Subject to changes of a technical nature