P2347 – Cylinder 12 Above Knock Threshold

System: Powertrain | Standard: ISO/SAE Controlled | Fault type: General | Location: Cylinder 12

Definition source: SAE J2012/J2012DA (industry standard)

P2347 indicates the control module has detected knock activity on cylinder 12 that exceeds an allowed threshold. This code does not, by itself, prove a specific failed part or a definite engine-damage condition; it describes what the module measured and how it classified that measurement. How the knock event is detected, filtered, and reported can vary by vehicle, including which sensors and signal-processing strategies are used. Always confirm the exact monitoring conditions, enabling criteria, and diagnostic flow in the appropriate service information before replacing parts or making calibration changes.

What Does P2347 Mean?

P2347 means Cylinder 12 Above Knock Threshold. In practical terms, the powertrain control module determined that the knock level attributed to cylinder 12 exceeded a calibrated limit during the conditions when the knock monitor is active. SAE J2012 defines how DTCs are structured and categorized, but the specific detection logic, thresholds, and required time or load conditions that trigger this code are vehicle-dependent. Use scan data and service information to verify when the code sets and what related parameters (such as spark control and knock feedback) were doing at the time.

Quick Reference

• System: Powertrain
• Official meaning: Cylinder 12 Above Knock Threshold
• Standard: ISO/SAE controlled
• Fault type: Plausibility
• Severity: MIL may illuminate, and the module may reduce performance by adjusting ignition timing to protect the engine.

Symptoms

• MIL/Check engine light: Light on or pending code stored after a drive cycle under load.
• Reduced power: Noticeable loss of acceleration if protective spark retard or torque limiting is applied.
• Rattle/ping: Audible knock under acceleration may be present, though it is not guaranteed.
• Roughness: Mild vibration or uneven feel, especially during higher load events.
• Poor fuel economy: Increased consumption due to retarded ignition timing or altered torque management.
• Hesitation: Brief stumble or delayed response during tip-in or climbing grades.
• Related codes: Additional misfire, fuel trim, or knock-related faults may appear depending on vehicle strategy.

Common Causes

• Low-octane/incorrect fuel for operating conditions: Fuel quality not supporting the engine’s current load, temperature, or calibration can contribute to knock being detected on a specific cylinder.
• Ignition system issues on cylinder 12: Worn or incorrect spark plug, weak ignition coil/boot, or poor terminal contact that promotes abnormal combustion events.
• Fuel delivery issue affecting cylinder 12: Injector restriction, electrical connection concern at the injector, or a cylinder-specific fueling imbalance that increases knock tendency.
• Air/fuel mixture imbalance: Unmetered air near that runner, intake sealing concerns, or sensor-driven fueling errors that make the mixture too lean under load.
• Mechanical contributors: Carbon deposits, combustion chamber hot spots, compression anomalies, or cooling-system-related cylinder temperature differences that elevate knock likelihood.
• Knock sensor or mounting concern: Sensor degradation, incorrect mounting torque/contact, or mechanical noise coupling that skews knock detection (design and sensor count vary by vehicle).
• Wiring/connector faults: Intermittent opens, shorts, corrosion, water intrusion, poor pin fit, or harness routing that affects knock sensor signal integrity or related engine sensor inputs.
• Power/ground integrity problems: Unstable sensor reference, shared ground issues, or excessive voltage drop impacting the PCM’s ability to interpret knock and control spark accurately.
• Control module or calibration issues: Less common; PCM software/logic or internal faults that misinterpret signals or apply incorrect cylinder-specific knock control (verify only after all basics pass).

Diagnosis Steps

Tools that help include a scan tool with live data and misfire/cylinder contribution information, a digital multimeter, and access to service information for cylinder numbering and connector pinouts. If available, an oscilloscope is useful for checking sensor and ignition waveforms. Basic hand tools, a good light, and supplies for cleaning/repairing terminals support accurate visual and physical inspections.

1. Confirm the code and capture freeze-frame: Scan for P2347 and any companion DTCs (misfire, fuel trim, knock sensor, coolant temperature, intake leaks). Record freeze-frame and operating conditions (load, RPM, temperature) to reproduce the event.
2. Verify cylinder 12 identification: Use service information to confirm cylinder numbering and bank layout (varies by vehicle). Misidentifying cylinder 12 can lead to incorrect parts swapping and missed root causes.
3. Check for obvious mechanical and intake issues: Inspect for vacuum/air leaks, loose intake ducting, cracked hoses, and signs of intake sealing problems that could create a lean cylinder condition near cylinder 12.
4. Evaluate fuel quality and operating conditions: Confirm the fuel is appropriate for the vehicle and conditions. If poor/incorrect fuel is suspected, document it and consider draining/refreshing fuel per service guidance before deeper electrical testing.
5. Review live data under the conditions that set the DTC: Road test or run the engine to mimic the freeze-frame scenario while logging knock-related PIDs (as available), spark advance, short/long fuel trims, misfire counters, coolant temperature, and load. Look for cylinder-specific misfire activity or abnormal fuel trim behavior that coincides with knock events.
6. Inspect ignition components for cylinder 12: Check spark plug condition and correct specification, inspect coil/boot for carbon tracking and terminal tension, and verify connectors are fully seated. If service information permits, swap ignition components with another cylinder and see whether the related symptom pattern follows the component (do not assume the DTC will “move”; validate with data).
7. Check cylinder 12 injector and circuit basics: Inspect injector connector pins for corrosion/poor fit and harness chafing. With key states as specified in service info, verify power feed presence, ground/control integrity, and continuity where applicable. Use voltage-drop testing on the power and ground paths while the circuit is loaded to uncover hidden resistance.
8. Inspect knock sensor(s) and related harness routing: Identify which sensor(s) are used for knock detection (varies by vehicle). Inspect connectors, harness routing near heat/sharp edges, and any shielding/retainers. Perform a wiggle test while monitoring knock signal-related PIDs to catch intermittent opens/shorts or noise coupling.
9. Assess cooling and combustion contributors: Confirm the engine reaches and maintains proper operating temperature and that there are no cooling system issues that could elevate cylinder temperatures. Inspect for signs consistent with carbon buildup or abnormal combustion. If indicated by symptoms/data, perform a relative compression test or cylinder leak check using manufacturer-approved procedures.
10. Use an oscilloscope if signals are suspect: If available, scope the knock sensor signal (and ignition primary/secondary if supported) during the event conditions. Look for abnormal noise, dropouts, or patterns that correlate with the DTC setting and with harness movement.
11. Recheck after corrections and validate with a drive cycle: After any repair, clear DTCs, repeat the same operating conditions, and confirm P2347 does not return. Verify trims, misfire counters, and knock-related parameters remain stable in the logged data.

Professional tip: Treat P2347 as a cylinder-specific knock detection event and prioritize reproducing the exact load/RPM/temperature conditions from freeze-frame. A clean road-test log that includes knock-related data, fuel trims, and cylinder misfire counters is often the fastest way to distinguish between true abnormal combustion on cylinder 12 and a signal integrity problem (wiring, grounds, or sensor noise).

Possible Fixes & Repair Costs

Repair cost for P2347 varies widely by vehicle and depends on what testing confirms, parts availability, and labor time to access cylinder-specific components. Avoid replacing parts based on the code alone; verify the root cause with targeted checks first.

• Correct fuel quality/condition: Drain/replace contaminated or incorrect fuel only if verified, and confirm the issue does not return after a controlled road test.
• Repair wiring/connectors: Fix damaged insulation, poor pin fit, corrosion, or loose connectors associated with the knock sensing and related engine harness routing (as applicable to the platform).
• Restore grounds and power feeds: Clean/secure ground points and repair power/ground distribution issues found during voltage-drop testing.
• Address ignition-related contributors: Replace worn spark plugs or ignition components only if inspection and misfire/combustion evidence supports it.
• Resolve air/fuel control issues: Correct vacuum/air leaks, injector issues, or sensor faults that testing shows are driving abnormal combustion and knock for the affected cylinder.
• Update or reprogram control module: Perform software updates or relearns only when service information calls for it and other faults are ruled out.
• Repair mechanical contributors: Correct confirmed mechanical problems (compression, cooling, deposits, or timing-related issues) that can elevate knock activity on the affected cylinder.

Can I Still Drive With P2347?

You may be able to drive short distances if the engine runs smoothly and no severe symptoms are present, but minimize load, avoid heavy acceleration, and monitor for worsening drivability. If you have reduced power, persistent misfire, overheating, abnormal knocking noise, stalling, or any safety-related warnings, do not drive; have the vehicle inspected to prevent engine damage.

What Happens If You Ignore P2347?

Ignoring P2347 can allow continued operation above the knock threshold on the affected cylinder, which may lead to escalating drivability issues and increased stress on engine components. Over time this can contribute to damage from abnormal combustion, higher emissions, and potential catalyst harm if misfire or fueling issues accompany the knock condition.

Last updated: February 17, 2026

Vehicles Commonly Affected by P2347

• Vehicles with 12-cylinder engine configurations: Platforms that support a cylinder 12 identifier in the powertrain control strategy.
• Performance-oriented calibrations: Powertrains tuned for higher load operation where knock control is frequently active.
• High-mileage engines: Greater likelihood of deposits, wear, or minor air/fuel/ignition degradations that can contribute to knock.
• Engines with complex intake routing: Increased chance of cylinder-to-cylinder airflow differences if leaks or restrictions develop.
• Direct-injection systems: Potential for deposit-related combustion changes and cylinder imbalance if maintenance is deferred.
• Vehicles operated under heavy load: Towing, high ambient temperatures, steep grades, or sustained high-speed driving can elevate knock tendency.
• Vehicles with prior wiring repairs: Harness routing, connector fitment, or ground integrity issues can appear after previous work.
• Vehicles with inconsistent fuel quality exposure: Repeated variation in fuel quality can increase knock events and adaptation limits.

For best results, focus on confirming why cylinder 12 exceeded the knock threshold under the recorded conditions, then re-test under similar load and temperature to verify the correction is durable.