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Home >> GMC >> 1998 >> Forward Control 6.5 Y, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System & Component Testing - 5.7L >> Ignition System >> Timing Control Systems >> Knock Sensor Circuit (Models Using Knock Sensor With Internal Spark Controller Module)
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Knock Sensor Circuit (Models Using Knock Sensor With Internal Spark Controller Module)

  1. An open or short circuit on knock sensor wire to PCM/VCM will set a related trouble code. A false detonation signal will not cause PCM/VCM to set a code.
  2. If a scan tool is available, connect it to Data Link Connector (DLC). Tap on engine next to knock sensor and note "knock" parameter. Knock should be indicated on scan tool.
  3. If a scan tool is not available, connect tachometer to engine. Start engine and hold RPM above idle. Using a metal object, tap on engine close to knock sensor. A noticeable decrease in engine RPM should occur. If no RPM decrease occurred, check knock sensor to PCM/VCM circuit.
  4. On vehicles equipped with automatic transmission, it may be necessary to place transmission in Drive for timing change to occur.
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