it wont help for 2 reasons one a 420 code is a matrix of calculations that the computer does to conclude if the o2 sensors are working correctly if they are there is only one other logical conclusion and that is the cat is not working up to par and thus u get the 420 code.
Reason 2 if u have a rich mixture like u say then u would get the 171 code because the computer would be dumping in more then 35% and that would start to damage the converter so if anything u would get the 171 codes b4 u would get the 420 code.

 

I have the same 0420 code and the dealer said the cat will be covered by warranty, but they have to charge me $500 for rear o2 sensor and to clean the throttle body... They said the throttle body is causing the cat problem along with the pcm. My question is, could i just take the throttle body off myself and clean it and then have them replace the cat and sensor? Or would a dirty throttle body even have anything to do with the cat needing to be replaced?

 

not a single thing with the cat issue

 

I wouldn't try to clean the throttle body unless u have done it before/also replacing o2 sensors u can do yourself/ and it doesn't matter if u get your parts from dealer or not/their parts are no better/ also have saw a lot of threads about advice costing/ my thought is that is what this form is for/ no one needs poor comments if u don't have anything to add then keep your info/ also if your throttlebody is dirty it could be the problem/ there is always something that u can try before u replace a cat/ get an emmision cleaner and replace both o2 sensors on the cat that is in question/and 500 bucks is high for o2 sensor and throttlebody cleaning/ it,s not rocket science? Thanks have a good day

 

Glad I found this post! My wife and I just got an 05 Pacifica that is throwing the 0420 code. Going to the dealer on Monday!. Hope they dont give me the run around!

 

I have a 06 T & C and have this code, and the light on.

Pep Boys changed the cat and three months later, this past Tues to be exact, heading to Daytona, the light came back on.

Took it to Advance and they plugged her in and got the same issue. They told me the light came on because of the cat, same thing as last time when the cat was replaced.

So, guess, its looking at the 02 sensor and/or wire harness next.

 

The guy with the bad cat should not replace it out of his own pocket. It is under warranty for 8 years or 80,000 miles

 

I'm going to add my quandary. I have the 420 code as well. I also get 455, 456, 457. As far as I know those are all vacuum leak codes. Autozone little code reader print out thing said 420 could be cause by large vacuum leak. I guess I am asking in this situation does the cat need to be replaced or is the vacuum leak just throwing everything off.

 

its separate systems the Cat is for the exhaust the other evap codes are for the vapor that the gas makes when it evaporates and the fed government does not like it to leak out in the ozone so completely separate systems

 

http://www.dodgeintrepid.net/showthr...ight=P0420+fix