Coolant Temperature Sensor

Depending on the engine, the coolant temperature sensor is installed at different locations. Observe the corresponding installation location. The coolant temperature sensor converts the temperature of the coolant and therefore of the engine oil into an electrical value (resistance). To do this, a resistance with negative temperature coefficient (NTC) is used. The coolant temperature is the measured variable for the following calculations, for example: Fuel injection rate and nominal idle speed.


Functional description


A temperature-dependent electrical resistor is used for temperature sensing. The circuit contains a voltage divider where the resistance can be measured depending on the coolant temperature sensor, whose resistance value drops when the temperature increases.


The resistance is temperature-dependent and varies between 217 kilo ohm and 37 ohm, which corresponds to a temperature of -55 to 155 degree C.


The resistance is dependent on the coolant temperature. A table that specifies the temperature associated with each resistance value is stored in the engine control. This compensates for the non-linear relationship between resistance and temperature.


Failure of the component


If the coolant temperature sensor fails, the following behavior is to be expected:

• Fault entry in the engine control unit
• Emergency operation with substitute value