P2337: Cylinder 2 Above Knock/Combustion Vibration Sensor Threshold
What to do
Check the fuel filler flap or the handbook for the grade the manufacturer specifies, and fill with it for a full tank before anything else is done. If the engine asks for premium and has been running on ordinary fuel, that alone causes this — the car is not damaged, but the module has been protecting it by retarding timing, which is why it feels flat and drinks more. That test costs one tank and eliminates the most common cause in this family. Avoid heavy loads meanwhile, and ease off if you hear a metallic rattle.
What this code means
Cylinder 2 is requiring more knock protection than the module considers normal. The mechanism and the per-cylinder reasoning are at P2336.
This is the right page for the single cheapest thing anyone can do about a knock code: use the fuel the engine was designed for.
Octane rating is a measure of a fuel's resistance to igniting spontaneously under pressure — which is precisely the thing knock is. A higher number does not mean more energy; it means the fuel will tolerate more compression before detonating. Engines are designed around a specific number, and turbocharged and high-compression engines are designed around a high one.
Filling an engine that specifies premium with ordinary fuel does not damage it, because the knock control will protect it — by retarding timing. The car simply becomes slower and thirstier, permanently and invisibly, and the money saved at the pump is partly given back in consumption. Where the margin is thin enough, the correction needed crosses the threshold and sets this code.
So the test is free and conclusive: fill with the specified grade, drive normally for a tankful, and see whether it clears. It costs one tank of fuel to eliminate the most common cause in the whole family, and it is worth doing before any part is bought.
Two related cases worth knowing. Fuel bought from a low-turnover station can be stale or contaminated and behave like a lower grade. And in some markets the ordinary grade varies seasonally, which explains a code that appears at one time of year and not another.
Likely causes
Start here
- Incorrect or low octane fuel · easy
- Stale or contaminated fuel · easy
- Carbon deposits in the combustion chamber · moderate
Less common
- Clogged fuel injectors · moderate
- Worn or fouled spark plugs · easy
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
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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