P2340
Cylinder 5 Above Knock/Combustion Vibration Sensor Threshold
Knock / combustion sensing
Generic OBD-II
Medium
What it means
P2340 means the knock sensor detected combustion knock (detonation) above the allowed threshold on cylinder 5. The ECM responds by retarding ignition timing, which protects the engine but reduces power. It's most often caused by low-octane fuel, carbon buildup, or an overheating/lean condition rather than a bad sensor — and persistent knock can eventually damage the engine, so it's worth addressing.
Medium
Can I keep driving? Usually yes, but the engine pulls timing and loses power; sustained knock can damage internals, so avoid hard acceleration until it's resolved.
Common symptoms
What you'll notice
- Check-engine light on
- Audible knock or pinging under load
- Reduced power (ECM retards ignition timing to protect the engine)
- Possible drop in fuel economy
Common causes
Most likely first
- Low-octane or poor-quality fuelLikely
- Carbon deposits in the combustion chamber raising compression/hot spotsCommon
- Overheating or a lean condition on that cylinderCommon
- Over-advanced ignition timingLess often
- Knock sensor reading noise or a genuinely faulty sensor (less likely for an 'above threshold' code)Less often
How to diagnose & fix
Work through it in order
- Fill up with the correct-octane, top-tier fuel and re-test — cheap or low-octane fuel is the most common trigger.
- Read freeze-frame data and check for related overheating or lean codes.
- Inspect for carbon buildup; consider an intake/combustion cleaning if mileage is high.
- Verify ignition timing and that cooling is working properly.
- Only if knock can't be confirmed mechanically, test the knock sensor circuit.
FAQ
Quick answers
Is it safe to drive with P2340?+
Light driving is usually okay, but knock (detonation) can damage pistons and rings over time. Avoid hard acceleration and heavy loads until you've traced the cause.
Can I just clear P2340?+
It returns if the engine is genuinely knocking. Try correct-octane fuel first; if it comes back, chase carbon, cooling, or timing issues.
Related codes
Often seen with P2340
Read & clear P2340 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