The PCM determines what cylinder to fire from the crankshaft position sensor input and the camshaft position sensor input. On 4-cylinder engines, the second crankshaft counterweight has two sets of four timing reference notches, including a 60 signature notch. From the crankshaft position sensor input, the PCM determines engine speed and crankshaft angle (position). On 6-cylinder engines, this sensor is a Hall effect device that detects notches in the flexplate.
The notches generate pulses from high to low in the crankshaft position sensor output voltage. When a metal portion of the notches line up with the crankshaft position sensor, the sensor output voltage goes low (less than 0.5 volts). When a notch aligns with the sensor, voltage goes high (5.0 volts). As a group of notches pass under the sensor, the output voltage switches from low (metal) to high (notch), then back to low.
If available, an oscilloscope can display the square wave patterns of each voltage pulse. From the width of the output voltage pulses, the PCM calculates engine speed. The width of the pulses represents the amount of time the output voltage stays high before switching back to low. The period of time the sensor output voltage stays high before switching back to low is referred to as pulse width. The faster the engine is operating, the smaller the pulse width on the oscilloscope.
On 4-cylinder engines, the crankshaft position sensor is mounted to the engine block behind the alternator, just above the oil filter. On 6-cylinder engines, the crankshaft position sensor is mounted on the transaxle housing, above the vehicle speed sensor.
To test this sensor, you will need the use of an oscilloscope. Visually check the connector, making sure it is attached properly and that all of the terminals are straight, tight and free of corrosion. Also inspect the notches in the crankshaft (4-cylinder) or flywheel (6-cylinder) for damage, and replace if necessary. The output voltage of a properly operating crankshaft position sensor switches from high (5.0 volts) to low (0.3 volts). By connecting an oscilloscope to the sensor output circuit, you can view the square wave pattern produced by the voltage swing.