P2347
Cylinder 12 Above Knock/Combustion Vibration Sensor Threshold
Ignition / knock control
Generic OBD-II
Medium
What it means
P2347 means the knock sensor detected combustion vibration on cylinder 12 above the allowed threshold — engine knock (detonation) the ECM couldn't fully correct. This code appears on twelve-cylinder engines and is often triggered by low-octane fuel, carbon buildup, overheating, or a lean mixture, though a faulty knock sensor can also cause it. Sustained knock can damage internal engine parts, so it's worth addressing.
Medium
Can I keep driving? Driveable, but sustained knock can damage pistons and bearings — use the correct octane and get it checked soon.
Common symptoms
What you'll notice
- Check-engine light on
- Audible knock or pinging, especially under load
- Reduced power (the ECM retards timing to protect the engine)
- Slightly reduced fuel economy
Common causes
Most likely first
- Actual detonation — low-octane fuel, carbon buildup, or overheatingLikely
- Lean air/fuel mixture or over-advanced ignition timingCommon
- Faulty knock sensor for cylinder 12 or a wiring/connector faultCommon
- EGR or cooling problems raising combustion temperaturesLess often
- Faulty ECM (rare)Less often
How to diagnose & fix
Work through it in order
- Fill with the manufacturer-specified octane and re-test — cheap fuel is a common trigger.
- Read freeze-frame and check for overheating, lean codes, or EGR faults alongside this code.
- Inspect the knock sensor connector and wiring for damage or corrosion.
- Check for carbon buildup and confirm ignition timing is within spec.
- Replace the knock sensor only after ruling out real detonation; clear and re-test.
FAQ
Quick answers
Is it safe to drive with P2347?+
Light driving is usually okay, but real, sustained knock can damage the engine. Avoid heavy loads and fix it soon.
Can I just clear P2347?+
You can, but it returns until the underlying knock or the sensor fault is resolved.
Related codes
Often seen with P2347
Read & clear P2347 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX