300, 300C & Magnum 2006-2008, Charger 2006-2008

Knock Sensor

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Operation



Two knock sensors are used; one for each cylinder bank. When the knock sensor detects a knock in one of the cylinders on the corresponding bank, it sends an input signal to the Powertrain Control Module (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 crystal's 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 the knock sensor voltage signal as an input. 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 short term and long 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 at Wide Open Throttle (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.

Removal & Installation



2.7L Engine
  1. Disconnect negative battery cable.
  2.  
  3. Remove the intake manifold.
  4.  
  5. Remove the passenger side cylinder head, refer to the engine section.
  6.  
  7. Disconnect the electrical connector from knock sensor.
  8.  
  9. Use a crow-s foot socket to remove the knock sensor.
  10.  

To install:

  1. Install the knock sensor. Tighten sensor to 7 ft. lbs. (10 Nm).
    WARNING
    Over or under tightening effects knock sensor performance resulting in possible improper spark control.

  2.  
  3. Attach the electrical connector to knock sensor.
  4.  
  5. Install the passenger side cylinder head, refer to the engine section.
  6.  
  7. Install the intake manifold.
  8.  
  9. Connect the negative battery cable.
  10.  

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.
  8.  

To install:

  1. Install knock sensor. Tighten knock sensor to 15 ft. lbs. (20 Nm).
    WARNING
    Over or under tightening effects knock sensor performance resulting in possible improper spark control.

  2.  
  3. Route the knock sensor wire in the proper location.
  4.  
  5. Install the intake manifold.
  6.  
  7. Reconnect knock sensor electrical connector.
  8.  
  9. Connect the negative battery cable.
  10.  

5.7L Engine
  1. Raise and support the vehicle.
  2.  
  3. Disconnect knock sensor electrical connector.
  4.  
  5. Remove the sensor mounting bolt. Note foam strip on bolt threads. This foam is used only to retain the bolts to sensors for plant assembly. It is not used as a sealant. Do not apply any adhesive, sealant or thread locking compound to these bolts.
  6.  
  7. Remove knock sensor from the engine block.
  8.  

To install:

  1. Thoroughly clean the knock sensor mounting hole.
  2.  
  3. Install knock sensor into cylinder block.
    WARNING
    Over or under tightening the sensor mounting bolts will affect knock sensor performance, possibly causing improper spark control. Always use the specified torque when installing the knock sensors. The torque for the knock sensor bolt is relatively light for an 8mm bolt.

  4.  
  5. Install and tighten mounting bolt to 15 ft. lbs. (20 Nm).
  6.  
  7. Install the knock sensor electrical connector.
  8.  

Testing



2.7L, 3.5L & 5.7L Engines
  1. Start the engine and allow it to reach normal operating temperature.
  2.  
  3. With the scan tool, select view DTCs.
    NOTE
    It may be necessary to test drive the vehicle within the DTC monitoring conditions in order for this DTC to reset.

  4.  
  5. If the DTC is Active or Pending at this time. Turn the ignition off.
  6.  
  7. Disconnect the Knock Sensor (KS) harness connector.
  8.  
  9. Disconnect the PCM harness connector.
  10.  
  11. With the ignition on, engine not running.
  12.  
  13. Measure the voltage on the (K42) KS number (1) signal circuit in the KS harness connector.
  14.  
  15. If there is any voltage present repair the short to voltage in the (K42) KS number (1) signal circuit.
  16.  
  17. If voltage was not present measure the resistance of the (K42) KS number (1) signal circuit from the KS harness connector to the appropriate terminal of pin out box tool 8815.
  18.  
  19. The resistance reading should be below 5.0 ohms.
  20.  
  21. If reading is not as stated repair the open in the (K42) KS number (1) signal circuit.
    WARNING
    Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install pin out box tool 8815 to perform diagnosis.



    Click image to see an enlarged view

    Fig. Knock Sensor (KS) harness connectors and wiring

  22.  

 
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