The camshaft position sensor in your car or light truck operates on the principle of magnetic induction. When a magnetic field collapses around a conductor, it induces a voltage into the conductor. In the camshaft sensor, a magnetic field, supplied by a permanent magnet in the sensor, is allowed to surround a conductor in the sensor. As the camshaft turns, a toothed gear on the camshaft passes through the field and causes it to collapse. The result is an A/C sine wave voltage that the on-board computer uses to determine camshaft position.
Unplug the electrical connector from the end of the sensor and remove the sensor. Consult your service manual for the exact procedures specific to your car as they vary from car to car. The typical camshaft position sensor is a cylindrical-shaped device, about 3 inches long and installed in the side of the engine block. The sensor must be removed for resistance testing with a multimeter.
Test for resistance by setting the multimeter to ohms and touching the two probes of the meter to the two pins in the electrical socket on the sensor. If resistance is infinite or 0 ohms, replace the sensor. Infinite resistance indicates an open circuit in the sensor, and 0 ohms indicates a shorted coil in the sensor.
Compare resistance measurements other than 0 ohms and infinite to the specifications for the sensor in the service manual. Replace the sensor if it does not fall within the specified range indicated in the service manual.