What is a spark plug defouler and what does it do?

I’ve read on some forums that you can use a defouler instead of getting new spark plugs. What is a spark plug defouler and what does it do?

Bonnie Stinson · Updated on
Reviewed by Shannon Martin, Licensed Insurance Agent.
Glad you asked! A defouler is an aftermarket component that can trick the O2 sensor by creating flow for fuel vapors, even if the spark plugs are dirty.
The defouler screws onto the spark plugs and acts as a sleeve, creating room for vapors and preventing spark plug damage. A clogged spark plug will prevent healthy combustion and may cause problems when
passing emissions testing
Some people choose to add the spark plug defouler to an O2 sensor, tricking it into appearing perfectly functional—and thus removing the P0420 code, which is a low catalyst efficiency system warning. To be clear, this is rigging the vehicle and it’s not legal.
A better solution is to replace your old spark plugs.
Hope this helps!
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Jerry partners with more than 50 insurance companies, but our content is independently researched, written, and fact-checked by our team of editors and agents. We aren’t paid for reviews or other content.

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