I replaced my cat 9 months ago ( after market cat)and have 19,000 miles on the cat. the car has 160,000 miles on it. The oxygen sensors have never been replaced. I am going to replace the two oxygen sensors with denso. Will that get rid of the 420 code. The car has a California cat.

 

the cat is under warranty federal law get it replaced again and replace rear 02 sensor

 

I have 25,000 mile warranty on the cat. I took it back were it was installed and they want me to replace the 2 sensors first. That is what i am doing . They wanted me to replace the sensors with( honda) three times the price of denso. Denso is oem direct replacement. Honda uses denso brand as original equipment. I told the repair shop if changing the sensors and the 420 code comes back then the cat is bad.

 

P0420 = Cat efficiency not 02 lean or rich or not responding, its a convertor issue not an 02 sensor issue there obligated by law to replace the cat at no charge to you. they should also warranty and not charge for scanning the car to cime up with this code