Pacifica, 2003-2005

Knock Sensor

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Operation



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 constantly vibrates and sends an input voltage (signal) to the PCM while the engine operates. As the intensity of the crystals vibration increases, the knock sensor output voltage also increases.

The voltage signal produced by the knock sensor increases with the amplitude of vibration. The PCM receives as an input the knock sensor voltage signal. If the signal rises above a predetermined level, the PCM will store that value in memory and retard ignition timing to reduce engine knock. If the knock sensor voltage exceeds a preset value, the PCM retards ignition timing for all cylinders. It is not a selective cylinder retard.

The PCM ignores knock sensor input during engine idle conditions. Once the engine speed exceeds a specified value, knock retard is allowed. Knock retard uses its own long-term and short-term memory program.

Long-term memory stores previous detonation information in its battery-backed RAM. The maximum authority that long term memory has over timing retard can be calibrated. Short-term memory is allowed to retard timing up to a preset amount under all operating conditions (as long as rpm is above the minimum rpm) except WOT. The PCM, using short-term memory, can respond quickly to retard timing when engine knock is detected. Short-term memory is lost any time the ignition key is turned off.


NOTE
mproper tightening affects sensor performance, possibly causing improper spark control.

Removal & Installation



3.5L Engine
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the upper intake manifold.
  4.  
  5. Disconnect the electrical connector.
  6.  
  7. Remove the knock sensor.

    Click image to see an enlarged view

    Fig.

  8.  

To Install:


NOTE
Improper tightening affects sensor performance, possibly causing improper spark control.

  1. Install knock sensor. Tighten knock sensor to 20 Nm (15.2 inch lbs.) torque.
  2.  
  3. Route the knock sensor wire in the proper location.
  4.  
  5. Install the upper intake manifold.
  6.  
  7. Connect the electrical connector.
  8.  
  9. Connect the negative battery cable.

    Click image to see an enlarged view

    Fig.

  10.  

3.8L Engine
  1. Disconnect the negative battery cable.
  2.  
  3. Raise vehicle and support.
  4.  
  5. Disconnect the electrical connector.
  6.  
  7. Remove mounting bolt and sensor.

    Click image to see an enlarged view

    Fig.

  8.  

To Install:

  1. Install knock sensor. Tighten knock sensor to 20 Nm (15.2 inch lbs.) torque.
  2.  
  3. Route the knock sensor wire in the proper location.
  4.  
  5. Connect the electrical connector.
  6.  
  7. Lower vehicle.
  8.  
  9. Connect the negative battery cable.

    Click image to see an enlarged view

    Fig.

  10.  

 
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