What Does P2339 Mean?
Cylinder 4 Above Knock Threshold indicates the knock sensor system has detected persistent detonation on cylinder 4 exceeding the ECM's maximum knock correction capability. The ECM has retarded timing to its limit but knock events continue to be detected on this cylinder.
Common Causes
30%
Carbon deposits on cylinder 4 piston or head creating hot spots
25%
Fuel injector 4 partially restricted or failing
25%
Knock sensor or circuit fault causing false knock detection
20%
Incorrect or low-quality fuel causing pre-detonation
Diagnostic Steps
1
Step 1: Monitor per-cylinder knock retard values. Compare cylinder 4 to all others to determine if the issue is isolated.
2
Step 2: Check fuel trim data and injector pulse width for cylinder 4. A shorter pulse width or higher fuel trim suggests a lean condition.
3
Step 3: Perform a cylinder leak-down test on cylinder 4 to check for abnormal sealing or elevated compression from carbon.
4
Step 4: Verify knock sensor output with an oscilloscope. Normal background noise should be distinguishable from actual knock events.
5
Step 5: If carbon buildup is confirmed, perform an appropriate decarbonization procedure and retest.
Estimated Repair Cost
$100 - $600
Parts + labor, varies by vehicle and location
Cylinder 4 Above Knock Threshold indicates the knock sensor system has detected persistent detonation on cylinder 4 exceeding the ECM's maximum knock correction capability. The ECM has retarded timing to its limit but knock events continue to be detected on this cylinder.
The most common cause of P2339 (Cylinder 4 Above Knock Threshold) is: Carbon deposits on cylinder 4 piston or head creating hot spots
Typical repair costs for P2339 range from $100 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Persistent detonation can lead to piston ring land failure or connecting rod bearing damage. Limit load and repair as soon as possible.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P2339 to identify the root cause.
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Quick Info
Category
Powertrain
System
Ignition/Combustion System
Difficulty
Type
Generic (SAE)
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