This might be reaching, but when I replaced my exhaust, at the same time I replaced my fuel filler cap with a locking one. The engine light came on. I did'nt lock the cap because it tightens better unlocked, no more engine light.Just a wild thought................Kevin.

 

Took the truck to the dealer this morning and they scanned it and the code that came up is P0420. They said the code could be related to a few things such as the sensors on the catalytic converter or a exhaust leak or it being i changed out the existing muffler. They had to reset to computer to clear the code. But they did say that type of code stores it self and could come back. Actually the dealer was really cool about it. Thank you all for your input.

 

Of course they are cool about it cuz when you come back with another problem they will relate it to the exhaust youwill pay cash no warranty and they make the whole cost no sharing with Fiat or whoever, I would feel like I was being set up.

 

yea man hate to say it, but they could rape you later. that code met a bad gas cap on my last ram. cost $100 for the dealer to tell me I needed a new $10 gas cap

 

I didn't have the light come on when I swapped the muffler on my truck, but when I swapped it on my car, the light came on almost right away. It was a 03 Chev Cav, and the muffler shop told me that it would come on because the muffler was apparently a "racing" muffler that was not approved for on road use. Anyways, I just kept driving it that way and the light went out. My guess was that one of the sensors picked up an increase in air flow that was different than what it was programed for and lit up the light. I was told that the computer would eventually adjust for the increased air flow and the light would go out, which it did. I thought that maybe it just burned out but after pulling the battery and hooking it back up, the light would come on for about 100kms, then go out again.

 

my guess is the inside of the muffler is burning the paint or whateveris in there and the sensors may be picking it up the extra flow shouldnt affect it cuz the airflow isnt constant

 

You'll often get a CEL when going to high flow cats or even sometimes with a muffler with a very good CFM rate, but a Flowmaster doesn't flow any better than the stock muffler, so I'd say they got a bad weld and an exhaust leak somewhere that's popping an O2 sensor if I were to guess.

I wouldn't take it to the dealer, they are gonna charge you a diagnostic fee and again to fix the problem. This is a result of modifications made to the vehicle so warranty ain't gonna cover it. Take it back to the muffler shop and tell them to make it right!