The knock sensor listens for engine "knock" — abnormal combustion that sounds like light pinging or rattling under load — and tells the computer to retard ignition timing when it hears it. If this sensor's circuit fails, the computer loses that protection and defaults to a more conservative, less efficient timing map to stay safe.
Symptoms
- Noticeably reduced power and slightly worse fuel economy (the computer is playing it safe)
- No knocking or pinging sound itself — that's what the sensor would have caught
- Sluggish acceleration compared to normal
- Sometimes no perceptible symptom at all besides the warning light
Likely causes
- Failed knock sensor — these are known to degrade with age and engine heat/vibration on many engines
- Damaged or corroded wiring/connector to the sensor
- Incorrect torque on the sensor's mounting bolt affecting its ability to sense vibration accurately
- A genuinely knocking engine (from carbon buildup, wrong-octane fuel, or an overheating issue) that's simply being detected correctly, not a sensor fault
How to diagnose it
- Check wiring and connector condition at the sensor first
- Test the sensor's resistance/output against spec with the sensor removed
- Rule out an actual engine knock issue (carbon buildup, low-octane fuel) before assuming the sensor itself is at fault
Typical fixes & cost
- Replace the knock sensor90–300 EUR
- Repair wiring or connector60–200 EUR
- Carbon/intake cleaning, if genuine knock from deposits is the underlying cause100–300 EUR
Code names are compiled from open/standardized SAE and ISO references. Explanations, symptoms, causes and fixes are original. Covers generic (P0/C0/B0/U0) codes only — manufacturer-specific codes are planned for a future update.
AS
Reviewed by Artyom SemenovAutomotive Editor · Fact-checked by Yauheni Kapliarchuk, Editor-in-Chief