Cylinder 5 Above Knock Threshold
The P2340 code means the vehicle's onboard diagnostic system has detected: Cylinder 5 Above Knock Threshold. This is a serious severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- hard
- Estimated cost
- $0 - $600 for the common causes (fuel, cleaning, an injector); engine damage repair costs far more - which is why this code should not be ignored
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Common Symptoms
- Check Engine Light on
- Pinging, rattling, or knocking - most audible under load or acceleration
- Reduced power as the PCM retards timing to protect the engine
- May occur with no audible symptom at all
Probable Causes (Ranked by Likelihood)
- Low-octane or contaminated fuel High
- Carbon buildup raising compression in cylinder 5 High
- Lean condition in this cylinder (injector, intake leak) causing hot combustion Moderate
- Cooling problem - a hot cylinder knocks first Moderate
- Over-advanced timing from a tune or a failing sensor Low
Frequently Asked Questions
What does P2340 mean?
P2340 means the knock sensor detected detonation in cylinder 5 beyond the allowed threshold. The PCM is already retarding timing to protect the engine - the code tells you protection was needed.
Can I keep driving with P2340?
Gently and briefly. The PCM's timing retard protects the engine at the cost of power, but sustained detonation is how pistons crack. Avoid heavy load and hard acceleration until it is diagnosed.
Is P2340 just a sensor problem?
Usually not. A faulty knock sensor sets its own circuit codes (P0324-P0334 range). This code means the sensor is working and heard real knock - treat the knock as genuine until proven otherwise.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
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Take this code seriously - sustained knock damages pistons and rod bearings.
-
Check fuel: right octane for the engine, and consider a fill from a different station.
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Read knock-retard and fuel trims on a scan tool; a lean trim on one bank narrows the cause.
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Check for other codes (injectors, MAF, coolant temperature) that would explain hot or lean combustion.
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If knock persists on good fuel, test compression and inspect for carbon buildup.
Sources 1
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
P2340 on Diesel, EV & Equipment
The same code ID appears across other engines and platforms. The diagnostic flow varies by manufacturer — these are the platform-specific breakdowns:
Commonly Affected Vehicles
- 2011-2017 Ford F-150 5.0L V8
- 2013-2021 Ford F-150 3.5L EcoBoost V6
- 2012-2020 Honda Accord 2.4L I4
- 2009-2017 Toyota Camry 3.5L V6
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