Crankshaft Position Sensor: Operation

The crankshaft position sensor detects slots cut into the transmission drive plate extension. See Fig 1. There are 3 sets of slots. Each set contains 4 slots, for a total of 12 slots. See Fig 2. Basic timing is set by the position of the last slot in each group. Once the Powertrain Control Module (PCM) senses the last slot, it determines crankshaft position (which piston will next be at TDC) from the camshaft position sensor input. The 4 pulses generated by the crankshaft position sensor represent the 69°, 49°, 29°, and 9° BTDC marks. It may take the PCM one engine revolution to determine crankshaft position.

Fig 1: Crankshaft Position Sensor

Courtesy of DAIMLERCHRYSLER CORP.

Fig 2: Timing Slots

Courtesy of DAIMLERCHRYSLER CORP.

The PCM uses crankshaft position reference to determine injector sequence, ignition timing and the presence of misfire. Once the PCM determines crankshaft position, it begins energizing the injectors in sequence.