Engine Temperature Sensor

The engine temperature input is provided by the NTC temperature sensor. The sensor contains two NTC elements. One is the engine temperature input to the engine control module, the other sensor is used for the instrument cluster's temperature gauge. The NTC functions as any NTC sensor found on the Bosch engine management systems. As the temperature increases, the resistance value of the NTC decreases. This produces a varying voltage signal input to the control module as a measure of the engine's coolant temperature.

The NTC is continuously monitored as part of the OBD II emission requirements. The parameters for monitoring of the input include:

- Upper and lower voltage limits
- Open circuits
- Plausibility of signal

If a malfunction occurs with the temperature input value, the control module will switch to a stored replacement value (FAIL-SAFE) for emergency running. The fault will be stored in memory and the Check Engine Lamp will illuminate when the OBD II criteria is satisfied.