P2347 — Cylinder 12 Above Knock Threshold #

Note: The description for DTC P2347 may vary depending on the vehicle manufacturer. Always consult your vehicle’s service information for model-specific definitions.

• P2347: Cylinder 12 Knock Detected Above Threshold (General, OBD-II Standard)
• P2347: Cylinder 12 Knock Sensor Circuit High Input (General Motors, GM)
• P2347: Cylinder 12 Excessive Knock Detected (Chrysler)
• P2347: Knock Control, Cylinder 12, Signal Too High (BMW)

Summary of DTC P2347 #

P2347 indicates that the engine control module (ECM) or powertrain control module (PCM) has detected knock levels in cylinder 12 that exceed the calibrated threshold. “Knock,” also known as detonation, refers to uncontrolled combustion in an engine cylinder, which can cause damage if persistent. The ECM uses information from the knock sensor—a piezoelectric device that detects vibrations—to monitor each cylinder’s combustion quality. If cylinder 12 consistently reports knock intensity higher than expected, this code is set. Some OEMs may use slightly different logic or thresholds, but the underlying concern is always excessive knock in a specific cylinder.

Common Symptoms for Code P2347 #

When P2347 is stored, you may notice various drivability symptoms. Sometimes, the check engine light is the only clue; in other cases, the car may run rough or lose power. Misfires and engine noises are also possible, especially under load or acceleration. In rare cases, no symptoms are present, but the issue should still be addressed to prevent long-term engine damage.

• Illuminated Check Engine Light (CEL)
• Rough engine idle or hesitation on acceleration
• Knocking or pinging noise from the engine—especially from cylinder bank 12 area
• Reduced engine power (limp mode possible on some OEMs)
• Poor fuel economy
• Possible engine misfire codes present

Most Likely Causes for P2347 #

This code is most often a sign of a genuine engine knock event or a fault in the knock detection circuit for cylinder 12. The causes can range from simple sensor issues to deeper internal engine problems. Here are the most common reasons, ordered from most to least frequent:

1. Bad or failing knock sensor on cylinder 12 (sensor physically degraded, wiring issue, or poor connection)
2. Incorrect fuel octane (using lower-than-recommended fuel, leading to premature combustion)
3. Engine mechanical problems (carbon build-up, hot spots, or valve timing issues)
4. Ignition timing too advanced (due to PCM/ECM software or faulty cam/crank sensors)
5. Lean air-fuel mixture (caused by vacuum leaks, fuel injector problems, or MAF sensor faults)
6. ECM/PCM malfunction (rare, but possible)

Step-by-Step Diagnostic for P2347 #

Diagnosing P2347 requires a logical, methodical approach. Begin with the basics—fuel quality and sensor wiring—before diving into complex engine internals. Follow these steps:

1. Confirm code and freeze frame data using a scan tool. Note when and under what conditions the code set.
2. Check for other related codes (misfires, fuel trim, O2 sensor errors) that could give more context.
3. Inspect knock sensor wiring and connector for cylinder 12. Look for damaged wires, corrosion, or loose pins.
4. Test knock sensor function with a multimeter or oscilloscope as per OEM specifications.
5. Verify fuel quality—ensure the fuel matches the manufacturer’s required octane rating.
6. Visually inspect engine for obvious issues (carbon buildup, vacuum leaks, leaking injectors).
7. Check ignition timing using scan data. Compare to OEM specs; check for recent software updates or sensor faults.
8. If all else checks out, perform a cylinder balance test and inspect for internal engine issues (valve, piston, or head gasket).

Possible Repairs for Code P2347 #

The repair for P2347 should always address the root cause, not just clear the code. Here’s what may be required depending on what the diagnosis reveals:

• Replace or repair knock sensor and wiring for cylinder 12
• Use correct fuel (drain tank and refill with recommended octane if necessary)
• Clean or decarbonize combustion chambers to remove hot spots
• Repair engine vacuum leaks or replace faulty fuel injectors/MAF sensor
• Update ECM/PCM software if TSBs (Technical Service Bulletins) apply
• Correct ignition timing (may require sensor replacement or timing adjustment)
• Repair internal engine faults (valve, piston issues—rare but possible if all else fails)

Can You Drive with Code P2347? #

Driving with P2347 is not recommended for extended periods. While the vehicle may run, persistent knock can cause severe engine damage over time—think of it as a ticking time bomb for your pistons and valves. If the check engine light is flashing or you hear audible knocking (pinging), stop driving immediately and seek repairs. If symptoms are mild, drive only as needed to seek service.

Vehicles Most Commonly Affected by P2347 #

P2347 is most frequently seen on modern V12 engines or V-configurations with 12 cylinders, especially in models that use individual cylinder knock sensing. Cylinder numbering and sensor locations may vary by OEM. Here are some platforms where this code may appear:

• BMW V12 engines (7 Series, 8 Series, 6.0L, 6.6L, 6.75L variants)
• Mercedes-Benz V12 engines (S600, SL600, Maybach, AMG V12s)
• General Motors V12 projects (rare, mostly commercial or prototype)
• Ferrari or Lamborghini V12 models (rare, code logic varies)
• Chrysler V12 applications (mostly marine or industrial)

Common Mistakes & Best Practices for P2347 #

When troubleshooting P2347, technicians and DIYers sometimes overlook simple causes or skip diagnostic steps. Rushing to replace sensors without proper testing can lead to wasted time and money. Here are some key pitfalls and tips:

• Replacing the knock sensor without checking wiring/connectors
• Ignoring fuel quality—always ask about recent fills or fuel changes
• Failing to review freeze frame data (it’s crucial for understanding when knock occurs)
• Missing related codes that point to root causes (misfires, lean conditions, etc.)
• Skipping OEM service bulletins or software updates

FAQ for Code P2347 #

Q: Can bad fuel alone trigger P2347?
A: Yes, using lower-octane fuel than recommended can cause real engine knock, triggering this code. Always use the correct fuel for your engine.

Q: Will clearing the code fix the problem?
A: Clearing P2347 without addressing the underlying cause will only temporarily turn off the check engine light. The code will return if the issue persists, and engine damage could occur if real knock continues.