GM Astro/Safari 1985-1996 Repair Guide

Knock Sensor

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OPERATION



See Figure 1



Click image to see an enlarged view

Fig. Fig. 1: The knock sensor informs the ECM when engine knock is occurring by producing a voltage via a piezoelectric crystal inside the housing

Located in the engine block, the Knock Sensor (KS) retards ignition timing during a spark knock condition to allow the ECM to maintain maximum timing advance under most conditions.

TESTING



  1. Connect a timing light to the vehicle and start the engine.
  2.  
  3. Check that the timing is correct before testing knock sensor operation.
  4.  
  5. If timing is correct, tap on the front of the engine block with a metal object while observing the timing to see if the timing retards.
  6.  
  7. If the timing does not retard, the knock sensor may be defective.
  8.  

REMOVAL & INSTALLATION



See Figure 2



Click image to see an enlarged view

Fig. Fig. 2: Engine knock sensor mounting location

  1. Disconnect the negative battery cable.
  2.  
  3. Disengage the wiring harness connector from the knock sensor.
  4.  
  5. Remove the knock sensor from the engine block.
  6.  

To install:
  1. Apply a water base caulk to the knock sensor threads and install the sensor in the engine block.
  2.  


WARNING
Do not use silicon tape to coat the knock sensor threads as this will insulate the sensor from the engine block.

  1. Engage the wiring harness connector.
  2.  
  3. Connect the negative battery cable.
  4.  

 
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