Does code P420 mean I need a new cat. converter??

Hello, Im new here and new to to doing my own car repairs. My engine light is on and when i had the codes pulled, 420 came up. I do hear a rattling by the cat. converter. Does anyone have any suggestions for me? Thank you. Dave.

P0420 - Catalyst System Efficiency Below Threshold (Bank 1)


That would be my guess

Before replacing the cat, try running a bottle of "Liquid Wrench Fuel Injection Cleaner".
That was an issue at a seminar recently.

Scratch that, I missed th "Rattle " part.
In that case thge cat is broken down/ melted internally. Time to replace it.

Code 420 does not always mean you you need a new cat.
Many things can cause a code 420 or 430. and even if the cat is bad you need to find out why it went bad.
No one cause of bad cats is bad tune up.
Also 02 sensors not working right can throw the code and some vechicles need a pcm reflash.
In your case if it is has the death rattle it need replaced.
You did not give year or mileage but.
Emmisions warranty cover them for 7 years or 70k
After that they are you pay.
Here is a site with a lot of good info on 420-430 codes
http://www.troublecodes.net/articles/catfailure/
MT-2500 :biggrin: