Subaru Coupes/Sedans/Wagons 1985-1996 Repair Guide

Knock Sensor (KS)

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OPERATION



When knocking occurs, the weight in the cylinder case moves, causing the piezo electric element in the KS to translate the vibration into an electric voltage. A signal is then transmitted from the KS to the ECU. In response, the control unit retards spark timing to prevent engine knocking.

On the Loyale with Multi-Point Fuel Injection (MPFI), the KS is located on top right-side of the cylinder block and senses knock signals from each cylinder.

On the Legacy and Impreza, the KS is installed on top left-side of the cylinder block and senses knock signals from each cylinder.

The SVX is equipped with 2 knock sensors; both are located on top of the cylinder block-one on the right side and one on the left side.

TESTING



Legacy, Impreza and SVX

See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: Testing the knock sensor

  1. Disconnect the KS harness.
  2.  
  3. Measure the resistance across the KS terminals.
  4.  
  5. The resistance should be approximately 560 kilo-ohms.
  6.  
  7. Replace the KS if the resistance is out of range.
  8.  

REMOVAL & INSTALLATION



  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the KS wire harness.
  4.  
  5. Loosen and remove the sensor retainer bolt, then remove the sensor.
  6.  

To install:
  1. Position the KS on the engine block, and secure in place with the retainer bolt. Tighten the bolt snugly.
  2.  
  3. Connect the sensor wire harness.
  4.  
  5. Connect the negative battery cable.
  6.  

 
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