More than likely the sensor is a thermistor. At room temperature the resistance will be around 2K ohms dropping to around 100 ohms as the temperature goes to 150 C. In a modern automobile one terminal probably goes to the ECM where it's connected through a resister to 5V. The other terminal is connected to ground. You will need to interface it to your Arduino through a high input impedance buffer so as not to affect the signal the ECM sees.