Crankshaft Position Sensor: Operation

Engine speed and crankshaft position are provided through the 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 crankshaft position sensor detects slots cut into the transmission driveplate extension. There are 3 sets of slots. Two sets contain 4 slots and one set contains 5 slots, for a total of 13 slots (Fig 1). 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 which piston will be next at TDC from the camshaft position sensor input. It may take the PCM one engine revolution to determine crankshaft position.

Fig 1: Timing Slots

Courtesy of DAIMLERCHRYSLER CORP.

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

The PCM uses the Crankshaft Position sensor to calculate the following:

• Engine rpm
• TDC number 1 and 4
• Ignition coil synchronization
• Injector synchronization
• Camshaft-to-crankshaft misalignment (Timing belt skipped 1 tooth or more diagnostic trouble code)