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Home >> GMC >> 1998 >> C3500 HD 6.5 F, Standard >> Repair and Diagnosis >> External Pages >> Different car >> Section 56 (Engine Controls - System & Component Testing 5.0L) >> Ignition System >> Timing Control Systems >> Knock Sensor Circuit (Models Using External Spark Controller Module)

Knock Sensor Circuit (Models Using External Spark Controller Module)

WARNING: This page is about a different car, the 1998 GMC Pickup and 1998 Chevrolet Pickup. However, it is still accessible from the selected car via links, so may be relevant.
  1. An open or short circuit on IC module control wire to PCM/VCM will cause a loss of 12-volt IC module signal. This will cause PCM/VCM to fully retard ignition timing.
  2. If a scan tool 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 tool.
  3. If a scan tool is not available, backprobe 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 PCM/VCM terminal should drop to zero volts, and return to original voltage when knock signal ceases.
  4. If voltage signal does not respond as described, check knock sensor-to-module-signal. On vehicles equipped with automatic transmission, it may be necessary to place transmission in Drive for timing change to occur.
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