Chrysler Neon 1995-1999 Repair Guide

Knock Sensor



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.

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


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.


See Figure 1

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

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.
  3. Attach the knock sensor electrical connector.
  5. Connect the negative battery cable.