What Does P2340 Mean?
Cylinder 5 Above Knock Threshold indicates the ECM detected excessive detonation on cylinder 5 beyond the knock correction limits. The ignition timing has been retarded to maximum for this cylinder, but knock events persist, indicating a mechanical or fuel delivery issue specific to this cylinder.
Common Causes
30%
Heavy carbon deposits in cylinder 5 combustion chamber
25%
Fuel injector 5 clogged or delivering insufficient fuel
25%
Knock sensor or wiring fault producing inaccurate readings
20%
Low-octane or contaminated fuel
Diagnostic Steps
1
Step 1: Compare per-cylinder knock correction values. If cylinder 5 shows substantially more retard than its neighbors, the issue is cylinder-specific.
2
Step 2: Evaluate fuel injector 5 performance with an injector balance test or by monitoring injector pulse width compared to other cylinders.
3
Step 3: Run a compression and leak-down test on cylinder 5. Compression higher than other cylinders suggests carbon accumulation.
4
Step 4: Check knock sensor mounting torque and wiring condition. Verify there are no external noise sources (loose brackets, accessory belt contact) that could be misinterpreted as knock.
5
Step 5: Treat carbon deposits with a top-engine cleaning procedure if confirmed as the root cause.
Estimated Repair Cost
$100 - $600
Parts + labor, varies by vehicle and location
Cylinder 5 Above Knock Threshold indicates the ECM detected excessive detonation on cylinder 5 beyond the knock correction limits. The ignition timing has been retarded to maximum for this cylinder, but knock events persist, indicating a mechanical or fuel delivery issue specific to this cylinder.
The most common cause of P2340 (Cylinder 5 Above Knock Threshold) is: Heavy carbon deposits in cylinder 5 combustion chamber
Typical repair costs for P2340 range from $100 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Continued knock can cause serious engine damage. Avoid high-load driving conditions and schedule repair promptly.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P2340 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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