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