I had my stock muffler removed and replaced it with a flowmaster super 40 series muffler. A couple of days later after the installation my engine light came on. So i took it to the dealer they scanned it and said it was a P0420 code. They cleared the code and said that type of code stores itself so it could come back on. Well Two days later after they cleared it driving home it came back on. Has anyone had this problem before? And how do you fix it? My truck only has 5,000 miles on it.

 

Think P0420 indicates a failed catalytic converter. You may have to check with the dealer to see what the cure is.

 

i agree with mike. i find it troubling that the dealer did not explain what the code was just that it would be back. i put a flowmaster original 40 on mine at about 1500 miles and i just crossed 14,000 last week and havent once had the light come on for anything. i would have the dealer do some investigating to find the cause.

 

I called the dealer this morning and told them the engine light came back on. And the asked me how hard would it be to put the stock muffler back on to so they could see if that eliminates the P0420 code. I told them i'm not paying to have the stock muffler installed then have the Flowmaster muffler put back on. By the way i had my resonators taken off, could that be a problem? My dealer said they were going to call there tech people and see if they heard of this problem before. This sucks!!!

 

Between the Super (loud) 40 and the resonator removal, you have significantly changed the back pressure and exhaust scavenging. Try putting the resonators back on and see if that is enough to fix it.

 

I agree with oldjeep. You have changed the pressure flow enough that I bet the two O2 sensors for the convertor are causing the problems. You may be stuck with fix engine light. Have you talked to flowmaster? If the cause if the change in exhaust, I will bet it will not be covered under warrenty.

 

Toss another handful of marbles in the "40" and turn it sideways, code should clear!