Chrysler Neon 1995-1999 Repair Guide

Crankshaft Position Sensor

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OPERATION



See Figure 1

The PCM determines what cylinder to fire from the crankshaft position sensor input and the camshaft position sensor input. The second crankshaft counterweight has two sets of four timing reference notches, including a 60° signature notch. 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 0.5 volts). when a notch aligns with the sensor, voltage goes 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.



Click image to see an enlarged view

Fig. Fig. 1: Timing reference notches

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° signature notch, the PCM calculates the crankshaft angle (position). In each group of timing reference notches, the first notch represents 69° Before Top Dead Center (BTDC). The second notch represents 49° BTDC. The third notch represents 29° BTDC. The last notch in each set represents 9° BTDC.

The timing reference notches are machined at 20° increments. From the voltage pulse width, the PCM tells the difference between the timing reference notches and the 60° signature notch. The 60°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° signature notch passes under the crankshaft position sensor, the PCM knows cylinder number on is the next cylinder at TDC.

The crankshaft position sensor is mounted to the engine block behind the alternator, just above the oil filter.

TESTING



See Figure 2

To test this sensor, you will need the use of an oscilloscope.

Visually check the connector, making sure it is attached properly and all of the terminals are straight, tight and free of corrosion.

The output voltage of a proper operating camshaft or crankshaft position sensor switches from high (5.0 volts) to low (0.3 volts). By connecting an oscilloscope to the sensor output circuit, you can view the square wave pattern produced by the voltage swing.



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Fig. Fig. 2: View of an oscilloscope's square wave pattern, in crankshaft degrees

REMOVAL & INSTALLATION



See Figure 3

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the crankshaft position sensor electrical connector.
  4.  
  5. Unfasten the sensor mounting screw, then remove the sensor from the vehicle.
  6.  



Click image to see an enlarged view

Fig. Fig. 3: The crankshaft position sensor is mounted to the engine block, behind the alternator just above the oil filter

To install:
  1. Install the sensor in the vehicle and secure with the retaining screw.
  2.  
  3. Attach the crankshaft position sensor electrical connector.
  4.  
  5. Connect the negative battery cable.
  6.  

 
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