2005 Hummer H2 4D Utility PickupFACTORY OEM SERVICE PROCEDURE

Detonation/Spark Knock

Detonation/Spark Knock

Inspection/Tests Action
DEFINITION: A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with throttle opening.
Preliminary Inspections
  • Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine ControlsΒ .
  • Search for bulletins.
  • Verify that the powertrain control module (PCM) grounds are clean, tight, and in the proper locations. Refer to Power and Grounding Component Views in Wiring Systems and Engine Controls Schematics .
  • If there are no engine mechanical faults, fill the fuel tank with a known high quality fuel that meets the vehicles minimum octane requirements. Road test the vehicle and re-evaluate the vehicles performance.
Fuel System
Ignition System Verify that the spark plugs are of the proper heat range. Refer to Spark Plug Inspection .
Engine Cooling System Inspect for obvious overheating problems:
  • Low engine coolant - Refer to Loss of Coolant in Engine Cooling for the type and amount of engine coolant to be used.
  • Restricted air flow to the radiator or restricted coolant flow through the radiator.
  • Inoperative cooling fan - Refer to Fan Clutch Diagnosis in Engine Cooling.
Engine Mechanical Inspect for the following engine mechanical problems:
Additional Inspections
  • Inspect the park/neutral position (PNP) switch operation. Refer to Diagnostic System Check - Vehicle in Vehicle DTC Information.
  • Inspect the transmission torque converter clutch (TCC) operation. The TCC applying too soon can cause the engine to spark knock. Refer to Diagnostic System Check - Vehicle in Vehicle DTC Information.
Factory Service Tools

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • β€’ You smell fuel, burning insulation, or see smoke.
  • β€’ Brakes feel soft, pull hard to one side, or make grinding noises.
  • β€’ The engine overheats, stalls repeatedly, or misfires under load.
  • β€’ You are missing required tools, torque specs, or safe lifting equipment.
  • β€’ You are not confident in the next step or safety outcome.

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