GM Full Size Vans 1987-1997 Repair Guide

Knock Sensor

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OPERATION



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



See Figure 1

  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.  



Click image to see an enlarged view

Fig. Fig. 1: Knock sensor wiring diagram

REMOVAL & INSTALLATION



  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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