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Home >> GMC >> 1998 >> Suburban K2500, 6.5 F >> Repair and Diagnosis >> External Pages >> Different car >> Section 116 (Engine Control System & Component Tests 6.5L Diesel) >> 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, 1998 GMC Cab & Chassis, 1998 Chevrolet Pickup, and 1998 Chevrolet Cab & Chassis. 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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