I have 1 2005 MC and my check engine light came on and it threw the code 0420. Everybody that I called and asked said that I needed a new cat, but i got a new cat, but it came back on again today. What could this mean?

 

[align=center]Hi Brian,[/align][align=center]It sounds like it could be a bad 02 sensor.[/align][align=center]Iwould reset your computer, and see if it returns, and if it[/align][align=center]does, I would have your sensors checked.[/align][align=center][/align][align=center]I hope that one of our experts tech members reads your post,[/align][align=center]and give you other possible solutions to your problem.[/align][align=center]Good Luck from[/align][align=center]`Space[/align][align=center][/align][align=center]Is you Monte Carlo smoking anything illegal ? and throwing the code 420 ?lol[/align]

 

What is the best way to reset my computer?

 

 

Thank you,

 

Did you get an aftermarket cat? If so, that's probably the problem.

 

So what do you suggest that I do at this point?

 

dustybird3 is right. Some aftermarket replacement cats just do not operate at the efficiency level that the software calibration in your Monte Carlo's powertrain control module expects. When I replace cats on my customers vehicles I only use OEM cats. Its one of the cases where the saying "you get what you pay for" really applies. What type of cat was installed on your Monte??

 

you could get either a 02 sensor emulator or a reprogrammed pcm with the code deleted.

 

I got an OEM Eastern Catalytic cat installed.So, would either the 02 sensor emulator or reprogrammed pcm work or is 1 preferred over the other? All of this information is greatly appreciated.