P2338
Cylinder 3 Above Knock/Combustion Vibration Sensor Threshold
Ignition / knock control
Generic OBD-II
Medium
What it means
P2338 means the knock (combustion vibration) sensor detected vibration from cylinder 3 above the allowed threshold — the signature of detonation, or a sensor reading it falsely. Common triggers are low-octane fuel, carbon buildup, or a lean/overheating condition. The engine still runs, but real knock left unchecked can cause mechanical damage, so diagnose it before driving hard.
Medium
Can I keep driving? Drivable, but don't lean on it — if real detonation is occurring, sustained hard driving can damage pistons; use the correct fuel and get it diagnosed.
Common symptoms
What you'll notice
- Engine knock or ping under load
- Reduced power (ECM may retard timing)
- Poorer fuel economy
- Check-engine light on
Common causes
Most likely first
- Low-octane or poor-quality fuelLikely
- Carbon buildup in cylinder 3Common
- Actual detonation from a lean mixture or overheatingCommon
- Faulty knock sensor or wiring giving false readingsLess often
- EGR or cooling issue raising combustion temperaturesLess often
How to diagnose & fix
Work through it in order
- Fill with the correct-octane fuel and re-test.
- Read knock and timing data to tell real detonation from sensor noise.
- Inspect the knock sensor, its wiring, and mounting torque.
- Check cylinder 3 for carbon buildup, a lean condition, or a cooling problem.
- Address the mechanical or fuel cause, then clear and re-test.
FAQ
Quick answers
Is it safe to drive with P2338?+
Short-term yes, but gently. If genuine detonation is happening, hard or sustained driving can damage the piston and rings on cylinder 3. Use good fuel and get it diagnosed.
Can I just clear P2338?+
It comes back if real knock continues or the sensor fault remains. Switching to the correct octane sometimes resolves fuel-related cases.
Related codes
Often seen with P2338
Read & clear P2338 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