P2347: Cylinder 12 Above Knock/Combustion Vibration Sensor Threshold
What to do
Avoid heavy loads and ease off if you hear a rattle. The thing to remember across all these codes is that hearing nothing is normal — the module keeps knock silent by retarding the timing, so a flat, thirsty engine is the usual symptom. If you do hear a sharp metallic rattle under acceleration, the protection has run out and easing off immediately is the right response. Check the specified fuel grade before anything is bought.
What this code means
Cylinder 12 is requiring more knock protection than normal — the last of the twelve, closing the family.
Worth restating once at the end, because it is the thing most worth carrying away: knock is one of very few engine faults where the driver's ear is a genuine diagnostic instrument, and where hearing nothing is the normal case. The module retards timing to keep knock inaudible, so a knock-prone engine presents as flat and thirsty rather than noisy. A driver who hears the sharp metallic rattle under acceleration is hearing the protection being exceeded, and that is the one moment in this family when the right response is immediate rather than considered: ease off.
The complementary block is at P0325–P0334, which reports faults in the knock sensor's circuit — the module unable to hear. This family reports what it heard.
Likely causes
Start here
- Incorrect or low octane fuel · easy
- Carbon deposits in the combustion chamber · moderate
- Clogged fuel injectors · moderate
Less common
- Faulty knock sensor · moderate
- Engine overheating · moderate
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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