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C-5, Knock Sensor Circuit (Models Using Knock Sensor With Internal Spark Controller Module)

WARNING: This page does not describe the selected car, but rather 10 other vehicles, including the 1994 GMC Vandura Special, 1994 GMC Vandura, 1994 GMC Rally Camper Special, 1994 GMC Rally, and 1994 GMC Forward Control. However, it is still accessible from the selected car via links, so may be relevant.
  1. An open or short circuit on knock sensor wire to ECM will set a related trouble code. A false detonation signal will not cause ECM to set a code.
  2. If a scan tester 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 tester.
  3. If a scan tester 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 ECM circuit.
  4. On vehicles equipped with automatic transmission, it may be necessary to place transmission in Drive for timing change to occur. See KNOCK SENSOR under ENGINE SENSORS & SWITCHES .
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