P2339

Cylinder 4 Above Knock/Combustion Vibration Sensor Threshold

Q: 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.

Q: 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.

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.

Real-world scan data

Seen in

scans in the past year

Found in

<0.1%

of scans

<0.1%

of scans that found faults

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

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.

Read & clear P2339 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX