What Does P2343 Mean?
Cylinder 8 Above Knock Threshold indicates the knock sensor system has detected detonation on cylinder 8 that exceeds the maximum allowable knock correction. The ECM has exhausted its timing retard strategy and knock continues, pointing to a mechanical or fuel delivery problem specific to cylinder 8.
Common Causes
30%
Excessive carbon accumulation on cylinder 8 piston and head
25%
Cylinder 8 fuel injector partially clogged or failing
25%
Knock sensor malfunction or wiring issue on bank 2
20%
Low-quality or incorrect octane fuel
Diagnostic Steps
1
Step 1: Compare per-cylinder knock retard across all 8 cylinders. Cylinder 8 showing significantly higher retard confirms isolated knock.
2
Step 2: Check bank 2 long-term fuel trim. Values above +10% indicate a lean condition contributing to detonation.
3
Step 3: Perform injector balance test on cylinder 8 and compare RPM drop to other cylinders.
4
Step 4: Test knock sensor 2 (bank 2) output signal with an oscilloscope during engine operation.
5
Step 5: If carbon is suspected, perform a top-engine decarbonization or intake valve cleaning (walnut blasting for direct-injection engines).
Estimated Repair Cost
$100 - $600
Parts + labor, varies by vehicle and location
Cylinder 8 Above Knock Threshold indicates the knock sensor system has detected detonation on cylinder 8 that exceeds the maximum allowable knock correction. The ECM has exhausted its timing retard strategy and knock continues, pointing to a mechanical or fuel delivery problem specific to cylinder 8...
The most common cause of P2343 (Cylinder 8 Above Knock Threshold) is: Excessive carbon accumulation on cylinder 8 piston and head
Typical repair costs for P2343 range from $100 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Continuous detonation will eventually damage pistons and bearings. Drive conservatively and repair before sustained high-load operation.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P2343 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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