By September 24, 2008 Read More →

Failed Emission Test – Codes P0420 P1131

My car did not pass smog in the state of California. It was diagnosed as a gross polluter. I have replaced oxygen sensors several times and still the check engine light comes on. The check engine light came on several years ago when I heard something fall down through the bottom of the car.

No one seems to fix it so the check engine light does not turn on again. I have been told it may be a cataylic converter and that the car has 2 to 3 of them. I would like some direction as to what could be the problem. The following I got off smog test:

Fault code P0420
CO (%) 4.15



Hi there Gloria,

I would suggest you look in your local phone book for a muffler shop in your area. Most muffler shops will install after market catalytic converters relatively inexpensive….or at least they do here in Texas, not real sure how your smog laws differ from ours. The muffler shop can test your converters to see which one is not working properly, I would assume it would be the driver side converter ( you have two of them) that has a problem.

You did not mention anything about the engine running badly, lack of power, engine missing etc. etc. etc. so I can only assume this is an emission system problem and not an actual “engine” problem. If the engine runs badly, you could have something wrong with a spark plug wire, injector or other engine control sensor.

Make some phone calls to muffler shops and get their opinion over the phone and get quotes for testing and replacing converters. I can get a converter replaced for about $175 here in Houston from a local muffler shop, and you might have to just take the plunge and replace one and see what happens.

Keep me posted as to what happens please, your response can help the next person.

Have a great week and keep your chin up.


Austin Davis

About the Author:

Austin Davis, consumer car repair advocate. "Hi there! I love to help people solve their car repair problems and I hope my site was helpful to you today. Thank you for stopping by."

Comments are closed.