P2340
Cylinder 5 Above Knock Threshold
The knock-sensor evaluation reports cylinder 5 above the knock threshold over a sustained window. The ECU retards ignition for that cylinder; persistent knock indicates poor fuel quality, carbon deposits or cooling issues.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Low octane or contaminated fuelCommon
- Carbon deposits raise compression locallyPossible
- Local cooling issue at cylinder 5Less likely
Parts involved
- Knock Sensor
- Cylinder 5
P2340 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.