Services
Insurance
Loans
Repairs
Advice
About

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?

avatar
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!
If you’re looking for ways to cut costs as a car owner, you might start by looking for a cheaper
car insurance
policy. Most people are needlessly overpaying for coverage—the free
Jerry
app can help you find out. Best of all, you’re just a few taps away from swapping to a cheaper policy.
View full answer 
WHY YOU CAN TRUST JERRY
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.

Join 4M+ members in lowering their car insurance

Easiest way to compare and buy car insurance

√
No long forms
√
No spam or unwanted phone calls
√
Quotes from top insurance companies
Find insurance savings — it's 100% free