Sunfire L4-138 2.3L DOHC VIN D MFI (1995)
Crankshaft Position Sensor: Description and Operation
PURPOSE
This system uses a magnetic Crankshaft Position (CKP) sensor, mounted remotely from the Ignition Control Module (ICM), which protrudes into
the block within approximately 0.050 inch from the crankshaft reluctor. The image shows a typical sensor in relationship to the crankshaft reluctor.
The reluctor is a special wheel cast into the crankshaft with seven slots machined in it, six of which are equally spaced 60 degrees apart. A seventh
slot is spaced 10 degrees from one of the other slots and serves to generate a "sync-pulse." As the reluctor rotates as part of the crankshaft, the
slots change the magnetic field of the sensor, creating an induced voltage pulse. The signal is necessary for the Powertrain Control Module (PCM)
to determine when to activate the fuel injectors.
OPERATION
Based on the CKP sensor pulses, the CKP sensor sends 7X reference signals to the PCM which is used to indicate crankshaft position and engine
speed. The CKP sensor continues to send these reference pulses to the PCM at a rate of seven times per 360 degrees of crankshaft rotation. This
signal is called the 7X reference because it occurs 7 times per crankshaft revolution.
By comparing the time between pulses, the PCM can recognize the pulse representing the seventh slot (sync pulse) which starts the calculation of
ignition coil sequencing. The second crank pulse following the "sync pulse" signals the PCM to fire the #2-3 ignition coil and the fifth crank pulse
signals the PCM to fire the #1-4 ignition coil.
