Chrysler Neon 1995-1999 Repair Guide

Knock Sensor

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OPERATION



See Figure 1

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

These vehicles are equipped with a knock sensor, which is threaded into the side of the cylinder block in front of the starter. When the knock sensor detects a knock in one of the cylinders, it sends an input signal to the PCM. In response, the PCM retards ignition timing for all cylinders by a scheduled amount.

Knock sensors contain a piezoelectric material which sends an input voltage (signal) to the PCM. As the intensity of the engine knock vibration increases, the knock sensor output voltage also increases.



Click image to see an enlarged view

Fig. Fig. 1: You can find the knock sensor in front of the starter, threaded into the side of the cylinder block

TESTING



A number of factors affect the engine knock sensor. A few of these are: ignition timing, cylinder pressure, fuel octane, etc. The knock sensor produces an AC voltage whose amplitude increased with the increase of engine knock. The knock sensor can be tested with a digital voltmeter. The RMS voltage at about 20mVac (at about 700 rpm) and increased to about 600mVac (5000 rpm). If the output falls outside of this range, a Diagnostic Trouble Code (DTC) will set.

REMOVAL & INSTALLATION



See Figure 1

  1. Disconnect the negative battery cable.
  2.  
  3. Unplug the electrical connector from the knock sensor.
  4.  
  5. Use a crow's foot wrench to remove the knock sensor from the vehicle.
  6.  

To install:
  1. Install the sensor in the vehicle and tighten to 7 ft. lbs. (10 Nm). Make sure not to over or under-tighten the sensor, as is could adversely effect knock sensor performance causing improper spark control.
  2.  
  3. Attach the knock sensor electrical connector.
  4.  
  5. Connect the negative battery cable.
  6.  

 
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