What Does P2338 Mean?
Cylinder 3 Above Knock Threshold means the ECM has detected detonation on cylinder 3 that exceeds the programmable knock correction limits. Even after applying maximum timing retard for this cylinder, the knock sensor continues to report knock events above the acceptable threshold.
Common Causes
30%
Excessive carbon buildup in cylinder 3 combustion chamber
25%
Cylinder 3 fuel injector restriction causing lean misfire and knock
25%
Knock sensor or wiring fault creating erroneous knock detection
20%
Low octane fuel or fuel contamination
Diagnostic Steps
1
Step 1: Review knock retard learning values for all cylinders. If cylinder 3 shows significantly more retard than others, the knock is cylinder-specific.
2
Step 2: Perform an injector balance test on cylinder 3. Compare RPM drop to other cylinders; a smaller drop indicates restricted flow.
3
Step 3: Check cylinder 3 compression. Elevated compression compared to other cylinders suggests carbon accumulation.
4
Step 4: Inspect knock sensor mounting and wiring integrity. Verify torque spec and check for loose connections.
5
Step 5: If carbon is confirmed, use a walnut shell blasting or chemical decarbonization method appropriate for the engine type.
Estimated Repair Cost
$100 - $600
Parts + labor, varies by vehicle and location
Cylinder 3 Above Knock Threshold means the ECM has detected detonation on cylinder 3 that exceeds the programmable knock correction limits. Even after applying maximum timing retard for this cylinder, the knock sensor continues to report knock events above the acceptable threshold.
The most common cause of P2338 (Cylinder 3 Above Knock Threshold) is: Excessive carbon buildup in cylinder 3 combustion chamber
Typical repair costs for P2338 range from $100 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Detonation causes progressive engine damage. Limit engine load and speed until the root cause is addressed. Prompt repair prevents costly internal engine damage.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P2338 to identify the root cause.
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Quick Info
Category
Powertrain
System
Ignition/Combustion System
Difficulty
Type
Generic (SAE)
Recommended Tools
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