Grand Cherokee 2WD V8-4.7L VIN J (2004)
The sensor is a hall effect device combined with an internal magnet. It is also sensitive to steel within a certain distance from it.
On the 4.7L V-8 engine, a tonewheel is bolted to the engine crankshaft. This tonewheel has sets of notches at its outer edge.
The notches cause a pulse to be generated when they pass under the sensor. The pulses are the input to the PCM.
