How to test hall effect sensors
electronic module image by Rob Hill from <a href='http://www.fotolia.com'>Fotolia.com</a>
The camshaft position sensor and the crankshaft position sensor are Hall effect sensors that monitor the position of the camshaft and the crankshaft. A small magnet passes in front of the sensor. As the magnet comes closer to the sensor, the output voltage rises.
As the magnet moves away from the sensor, the voltage decreases. The electronic control module (ECM) monitors these sensor outputs to determine shaft position. The camshaft and crankshaft position sensors, along with other electrical sensors, solenoids and injectors, allow the ECM to maintain precise engine control. Understanding the basic theory of Hall effect sensors will help you properly test a questionable sensor.
Remove the sensor from the engine block. Clean the sensor tip by removing oil, dirt and metal shavings.
Review the schematic for the engine and locate the camshaft sensor or crankshaft signal to the ECM. Remove the signal wire from the ECM. Connect one end of the jumper wire to the signal wire. Connect the other end of the jumper wire to the tip of the positive probe. Connect the negative probe on a good chassis ground connection. If needed, use a jumper with alligator clips to connect the negative probe to chassis ground.
Turn the digital voltmeter to measure DC volts. Turn the key switch "On." The voltage should be approximately 0 volts. Slowly move the magnet perpendicular to the front of the sensor. The voltage should increase as the magnet moves toward the sensor and decreases as it moves away. If the voltage does not change, there is a problem with the sensor or connections to the sensor.