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    Knock Sensor

    Inspect/Test/Replace

    WARNING
    Operating an engine with a detonation problem may result in piston, ring, and cylinder wall damage.

    The procedure for checking a knock sensor varies depending upon the vehicle make and year. Always follow the vehicle manufacturer's recommended test procedure and specifications. Follow these steps for a typical knock sensor diagnosis:

    • Connect a scan tool to the DLC and check for DTCs (diagnostic trouble codes) related to the knock sensor system.
      • If DTCs are present, diagnose the cause of these codes.
      • When no DTCs related to the knock sensor system are present, the system needs to be checked.
    Knock sensor and related voltage signal. Reprinted with the permission of the Ford Motor Company.
    • Some guidelines for testing the knock sensor and sensor circuit follow:
      • Make sure the engine is at its normal operating temperature.
      • If a knock sensor signal is present when the scan tool is first turned on, disconnect the wire from the knock sensor and observe the tester.
      • If the knock sensor signal is no longer present, the engine has an internal knock or the knock sensor is defective.
      • When the knock sensor signal is still present on the scan tool, check the wire from the knock sensor to the knock sensor module for picking up false signals from an adjacent wire.
      • Reroute the knock sensor wire as necessary.
      • If the knock sensor doesn't respond to the tapping on the engine, turn off the ignition switch and disconnect the knock sensor module wiring connector.
      • Use a high-impedance test light or ohmmeter to check the ground circuit.
      • If the ground circuit was found to be all right, reconnect the knock sensor module wiring connector, and disconnect the knock sensor wire.
      • Operate the engine at idle speed and momentarily connect a 12-volt test light from a 12-volt source to the knock sensor wire.
      • If a knock sensor AC signal is now generated on the scan tool, there is a faulty connection at the knock sensor or the knock sensor is defective.
      • When a knock sensor signal is not generated, check for faulty wires from the knock sensor to the module or from the module to the PCM.
      • If the wires and connections are satisfactory, the knock sensor module is likely defective.

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