As a passive sensor, the temperature sensor delivers information to the control unit about the momentary temperature of the coolant and thus of the engine.
Its resistance changes with the temperature. At a negative temperature coefficient (NTC), the ohmic resistance decreases as the temperature rises. This type of sensor is also called a 'hot-
lead'. As a passive element, it is dependent on the control device for a voltage. The voltage change caused by the resistance is a measure of the engine temperature.
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The resistances are accumulative. Should, e.g., an NTC-temperature sensor convey the coolant temperature to the control device and there is an additional resistance in play, it can happen that the fuei-air mixture is
over-enriched, this can, at least partialy, be compensated for by the Lambda-regulation.
The temperature sensor used to be called 'The General', because of it's decisive influence on the mixture formation. If, e.g., it shows a minus temperature in the double figures range, the injection time of, normally a
few milli-seconds when idling, can rise up to over 100. The car will then start only very unwillingly, or not at all. If the error continues for any length of time, the over-enrichment can have serious results for the engine. A
typical indication would be the penetrating smell of petrol. 02/12