Cobalt 2006-2008, G5 2007

Knock Sensor

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Operation



The Knock Sensor (KS) system enables the control module to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation. The control module uses the KS system to test for abnormal engine noise that may indicate detonation, also known as spark knock.

This KS system uses one or two flat response two-wire sensors. The sensor uses piezo-electric crystal technology that produces an AC voltage signal of varying amplitude and frequency based on the engine vibration or noise level. The amplitude and frequency are dependant upon the level of knock that the KS detects. The control module receives the KS signal through a signal circuit. The KS ground is supplied by the control module through a low reference circuit.

The control module learns a minimum noise level, or background noise, at idle from the KS and uses calibrated values for the rest of the RPM range. The control module uses the minimum noise level to calculate a noise channel. A normal KS signal will ride within the noise channel. As engine speed and load change, the noise channel upper and lower parameters will change to accommodate the normal KS signal, keeping the signal within the channel. In order to determine which cylinders are knocking, the control module only uses KS signal information when each cylinder is near top dead center (TDC) of the firing stroke. If a knock is present, the signal will range outside of the noise channel.

If the control module has determined that a knock is present, it will retard the ignition timing to attempt to eliminate the knock. The control module will always try to work back to a zero compensation level, or no spark retard. An abnormal KS signal will stay outside of the noise channel or will not be present. KS diagnostics are calibrated to detect faults with the KS circuitry inside the control module, the KS wiring, and the KS voltage output. Some diagnostics are also calibrated to detect constant noise from an outside influence such as a loose/damaged component or excessive engine mechanical noise.

Removal & Installation



  1. Disconnect the negative battery cable.
  2.  
  3. Remove the starter.
  4.  
  5. Disconnect the Knock Sensor (KS) harness connector.
  6.  
  7. Remove the KS retaining bolt.
  8.  
  9. Remove the KS.
  10.  

To install:


WARNING
Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.


NOTE
The KS threaded surfaces must be clean before installation.

  1. Install the KS. Tighten the KS retaining bolt to 18 ft. lbs. (25 Nm).
  2.  
  3. Connect the KS harness connector.
  4.  
  5. Install the starter:
    1. Tighten starter bolts to 37 ft. lbs. (50 Nm)-2.0L engine.
    2.  
    3. Tighten starter bolts to 30 ft. lbs. (40 Nm)-2.2L & 2.4L engines.
    4.  

  6.  
  7. Connect the negative battery cable.
  8.  

Testing





Click image to see an enlarged view

Fig. Knock Sensor (KS) connector end view-2.0L, 2.2L, & 2.4L engines

  1. Inspect the KS for physical damage. A KS that is dropped or damaged may cause a DTC to set.
  2.  
  3. Inspect the KS for proper installation. A KS that is loose or over torqued may cause a DTC to set. The KS should be free of thread sealant.
  4.  
  5. The KS mounting surface should be free of burrs, casting flash, and foreign material.
  6.  

Component Testing
  1. Connect the DMM from the KS signal circuit terminal A to the KS signal circuit terminal B on the sensor side of the KS harness connector. Set the DMM to the 400 mV AC hertz scale and wait for the DMM to stabilize at 0 Hz.
    WARNING
    DO NOT tap on plastic engine components.

  2.  
  3. Tap on the engine block with a non-metallic object near the KS while observing the signal indicated on the DMM. The DMM should display a fluctuating frequency while tapping on the engine block.
  4.  
  5. If the KS makes no response to the tapping, replace the KS.
  6.  

P0325, P0327, & P0328 DTC Codes
  1. With ignition ON, engine OFF:
    1. Disconnect the KS harness connector.
    2.  
    3. Measure for 2-3 volts between each of the following circuits and ground on the ECM side of the harness connector:

      The KS signal circuit, terminal A
       
      The KS signal circuit, terminal B
       

    4.  
    5. If less than the specified range, test the circuits for a short to ground or an open/high resistance. If the circuits test normal, you may need to replace the ECM.
    6.  
    7. If greater than the specified range, test the circuits for a short to voltage. If the circuits test normal, you may need to replace the ECM.
    8.  
    9. If the circuits test normal, replace the KS.
    10.  

  2.  

 
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