Grand Caravan L4-2.4L DOHC (1996)
Crankshaft Position Sensor: Description and Operation
Fig 1 Timing Reference Notches
OPERATION
The PCM determines what cylinder to fire from the crankshaft position sensor input and the camshaft position sensor input. The second crankshaft
counterweight has machined into it two sets of four timing reference notches and a 60 degree signature notch (Fig. 1). From the crankshaft position
sensor input the PCM determines engine speed and crankshaft angle (position).
The notches generate pulses from high to low in the crankshaft position sensor output voltage. When a metal portion of the counterweight aligns
with the crankshaft position sensor, the sensor output voltage goes low (less than 0.3 volts). When a notch aligns with the sensor, voltage switches
high (5.0 volts). As a group of notches pass under the sensor, the output voltage switches from low (metal) to high (notch) then back to low.
If available, an oscilloscope can display the square wave patterns of each voltage pulse. From the width of the output voltage pulses, the PCM
calculates engine speed. The width of the pulses represent the amount of time the output voltage stays high before switching back to low. The
period of time the sensor output voltage stays high before switching back to low is referred to as pulse width. The faster the engine is operating,
the smaller the pulse width on the oscilloscope.
By counting the pulses and referencing the pulse from the 60 degree signature notch, the PCM calculates crankshaft angle (position). In each group
of timing reference notches, the first notch represents 69 degrees before top dead center (BTDC). The second notch represents 49 degrees BTDC.
The third notch represents 29 degrees. The last notch in each set represents 9 degrees before top dead center (TDC).
The timing reference notches are machined to a uniform width representing 13.6 degrees of crankshaft rotation. From the voltage pulse width the
PCM tells the difference between the timing reference notches and the 60 degree signature notch. The 60 degree signature notch produces a longer
pulse width than the smaller timing reference notches. If the camshaft, position sensor input switches from high to low when the 60 degree
signature notch passes under the crankshaft position sensor, the PCM knows cylinder number one is the next cylinder at TDC.
Fig 8 Crankshaft Position Sensor
