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Home >> GMC >> 1996 >> Forward Control 4.3 W >> Repair and Diagnosis >> External Pages >> Different car >> Section 134 (Engine Controls - System/Component Tests - 7.4L) >> Ignition System >> Timing Control Systems (C-4 & C-5) >> C-5, Knock Sensor Circuit (Models Using External Spark Controller Module)
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C-5, Knock Sensor Circuit (Models Using External Spark Controller Module)

WARNING: This page does not describe the selected car, but rather 18 other vehicles, including the 1995 GMC Vandura Special, 1995 GMC Vandura, 1995 GMC Suburban, 1995 GMC Rally Camper Special, and 1995 GMC Rally. However, it is still accessible from the selected car via links, so may be relevant.
  1. An open or short circuit on ESC wire to ECM/PCM/VCM will cause a loss of 12-volt ESC controller signal. This will cause ECM/PCM/VCM to fully retard ignition timing.
  2. If a scan tester is available, connect tester to Data Link Connector (DLC). Using a metal object, 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, backprobe ECM/PCM/VCM knock sensor signal terminal with a DVOM. With engine idling, 8-12 volts should be present at this terminal. Using a metal object, tap on engine close to knock sensor. Voltage signal at ECM/PCM/VCM terminal should drop to zero volts, and return when knock signal ceases.
  4. If signal does not respond as described, check knock sensor-to-controller-signal. 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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