P2339: Cylinder 4 Above Knock Threshold

What it means

The knock sensor channel for cylinder 4 has registered combustion noise above the calibrated knock threshold beyond what the spark retard map can correct. Often associated with low-octane fuel, EGR malfunction or carbon-induced hot spots.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The knock-sensor signal lets the controller detect detonation and adjust ignition timing. This code identifies knock above the permitted threshold on the cylinder 4 channel despite timing correction, so the issue may be real cylinder 4 knock or a fault in that channel's sensor signal.

Common causes

Most likely first.

1. Abnormal combustion knock
2. Knock sensor or wiring fault

Symptoms

• Check-engine light
• Pinging or rattling under acceleration
• Reduced power or sluggish acceleration

How to diagnose it

1. Record freeze-frame data and review knock retard, engine load, and temperature when cylinder 4 exceeded the threshold.
2. Verify the fuel meets the manufacturer's required octane rating and note any recent change in fuel.
3. Check whether pinging occurs under the recorded conditions and look for overheating or other abnormal engine operation.
4. Inspect the cylinder 4 knock-sensor connector and harness for corrosion, looseness, or damage.
5. If the condition persists, test the cylinder 4 sensor circuit and investigate combustion deposits or faults according to the manufacturer's procedure.

Common fixes

• Refuel with fuel meeting the manufacturer's octane requirement.
• Repair damaged or loose cylinder 4 knock-sensor wiring or terminals.
• Correct any confirmed cooling or engine fault contributing to detonation.
• Replace the knock sensor if circuit testing confirms it is faulty.
• Resolve confirmed cylinder 4 deposits or combustion problems using the manufacturer's procedure.

Can I keep driving?

Avoid heavy load, towing, and hard acceleration while pinging continues because sustained detonation can damage the engine. Stop if the rattling is severe or persists at light load.