Alero L4-144 2.4L DOHC VIN T SFI (2000)
Crankshaft Position Sensor: Description and Operation
General Description
IMPORTANT: Perform a Crankshaft Position System Variation Learn procedure any time you make a change to the crankshaft sensor to crankshaft
relationship. Changing the crankshaft sensor to crankshaft relationship will not allow the PCM to detect a misfire at all speeds and loads accurately,
resulting in possibly setting a false misfire DTC. Removing a part for inspection and then reinstalling the same part is considered a disturbance. A false
DTC P0300 could set if you do not perform this procedure. Refer to Crankshaft Position System Variation Learning Procedure. See: Service and
Repair/CKP System Variation Learn Procedure
This system uses a magnetic CKP sensor, mounted remotely from the ICM, which protrudes into the block within approximately .050 in. of the
crankshaft reluctor. The reluctor is a special wheel cast into the crankshaft with 7 slots machined into the wheel, 6 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.
Based on the CKP sensor pulses, the ICM sends 7X reference signals to the PCM which is used to indicate the crankshaft position and the engine speed.
The ICM continues to send these reference pulse to the PCM at a rate of 7 per 360 degrees of crankshaft rotation. This signal is called the 7X reference
because it occurs 7 times per crankshaft revolution. The 7X reference signal is necessary for the PCM to determine when to activate the fuel injectors.
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.
