3.7L V-6
WARNING: This page is about a different car, the 2005 Jeep Grand Cherokee. However, it is still accessible from the selected car via links, so may be relevant.
Engine speed and crankshaft position are provided through the CKP (Crankshaft Position) sensor. The sensor generates pulses that are the input sent to the Powertrain Control Module (PCM). The PCM interprets the sensor input to determine the crankshaft position. The PCM then uses this position, along with other inputs, to determine injector sequence and ignition timing.
The sensor (3) is a hall effect device combined with an internal magnet. It is also sensitive to steel within a certain distance from it.
A tone wheel (target wheel) is bolted to the engine crankshaft (1). This tone wheel has sets of notches (2) 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.