Coolant Temperature Sensor
The coolant temperature sensor, like the intake air temperature sensor, is an NTC resistor
(Negative Temperature Coefficient).
This means: cold coolant temperature = high resistance
warm coolant temperature = low resistance
To increase the accuracy of the sensor, the temperature is probed in two measuring ranges. In the border range between 40 - 50 °C/104 - 122 °F, TECH 1 displays of two different voltages for one and the same temperature display are possible.
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TECH 1 display
| Coolant temp. | Coolant temp. |
|---|---|
| 45° 1.2 V | 45° 3.7 V |
A jump in voltage displayed by TECH 1 while the temperature remains the same (approx. 40 °C to 45 °C/ 104 °F to 113 °F) is therefore not the result of a loose contact; it is caused by the control unit selecting a measuring range.
The relationship between the coolant temperature and the resistance values can be taken from the table in the relevant Checking Procedures.
This characteristic corresponds to that of the intake air temperature sensor, described above.
The coolant temperature sensor cannot by replaced by the intake air temperature sensor, however.