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P2347Cylinder 12 Above Knock Threshold

The engine computer detected knock (detonation) in cylinder 12 that exceeded the allowable threshold despite its knock-control corrections.

Definition

On 12-cylinder engines, the PCM uses knock sensors to monitor combustion in each cylinder and retards ignition timing individually when knock is detected. This code sets when knock activity attributed to cylinder 12 exceeds the calibrated threshold beyond what timing retard can safely correct. Symptoms include reduced power from timing pullback, possible audible pinging under load, and an illuminated MIL. Sustained detonation can damage pistons, ring lands, and bearings, so the cause should be found promptly.

Common causes

  • Low-octane, stale, or contaminated fuel
  • Carbon buildup in cylinder 12 raising effective compression and creating hot spots
  • Lean condition on that cylinder from a vacuum leak or restricted injector
  • Engine running hot or localized cooling problem
  • Faulty knock sensor, incorrect sensor torque, or wiring fault falsely flagging knock
  • Mechanical noise near cylinder 12 (worn bearing, piston slap) misread as knock

Common misdiagnoses

  • Knock sensor replaced when the engine genuinely is detonating
  • Ignition coil or spark plug replaced for a combustion-quality problem
  • Injector replaced without confirming a lean condition on that cylinder
  • PCM replaced for what is a fuel-quality or carbon issue

Troubleshooting steps

  1. 1.Verify fuel quality and octane first

    Confirm the vehicle is running the manufacturer-required premium octane and try a fresh tank from a reputable station before deeper diagnosis.

  2. 2.Check for companion codes and scan data

    Lean codes, misfire counters, or fuel trims skewed on cylinder 12's bank narrow the cause; also watch per-cylinder knock retard PIDs under load.

  3. 3.Inspect cylinder 12's spark plug

    Speckled deposits, a blistered insulator, or signs of overheating confirm real detonation in that cylinder.

  4. 4.Check the cooling system

    Verify coolant level, thermostat operation, and that ECT readings are normal, since overheating promotes knock.

  5. 5.Evaluate carbon buildup

    On direct-injection engines especially, borescope the cylinder and consider an induction or combustion-chamber cleaning if deposits are heavy.

  6. 6.Test the knock sensor and wiring

    Confirm correct mounting torque and shielded wiring integrity — an over- or under-torqued sensor skews signal amplitude and can flag phantom knock.

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