P2339
Cylinder 4 Above Knock/Combustion Vibration Sensor Threshold
Ignition / knock control
Generic OBD-II
Medium
What it means
P2339 means the knock (combustion-vibration) sensor detected vibration above the allowed threshold on cylinder 4. That can be genuine detonation — from low-octane fuel, carbon, a lean mixture, or an overheating engine — or a faulty sensor. The ECM typically retards timing to protect the engine, which shows up as reduced power.
Medium
Can I keep driving? You can usually drive, but the engine may pull timing and feel down on power; heavy detonation can damage pistons, so don't ignore it.
Common symptoms
What you'll notice
- Reduced power as the ECM retards timing
- Pinging or knocking under load
- Slightly reduced fuel economy
- Check-engine light on
Common causes
Most likely first
- Actual detonation on cylinder 4 from low-octane fuel, carbon buildup, or lean mixtureLikely
- Engine running hot or an EGR fault raising combustion temperaturesCommon
- Faulty knock/combustion-vibration sensorCommon
- Knock sensor wiring or connector faultLess often
- Faulty ECM (rare)Less often
How to diagnose & fix
Work through it in order
- Rule out real detonation first: use the correct octane fuel, check cooling, and inspect for carbon buildup.
- Verify fuel trims and look for a lean condition or vacuum leak feeding cylinder 4.
- Inspect the knock sensor connector and wiring for damage or looseness.
- Test the knock sensor and replace it if it reads out of range.
- Clear the code and confirm the threshold is no longer exceeded.
FAQ
Quick answers
Is it safe to drive with P2339?+
Light driving is usually okay, but persistent knock can damage pistons and rings. Reduce load, use the right fuel, and get it diagnosed.
Can I just clear P2339?+
If the cause is real detonation it will return under load. Fix the underlying cause — fuel, cooling, or the sensor — before relying on a clear.
Related codes
Often seen with P2339
Read & clear P2339 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