Well...It's been a while since anything has went wrong with the truck...last thing I replaced was the EGR valve...now I have this code P0420...I know that it has something to do with the CAT but I am clueless as to what to do...I'm reading mixed emotions about this issue...a few guys said that this issue appears at extreme cold temps..which have came into Indiana...I'm wondering if this is an actual problem or if the computer is tripping a false alarm...I'm not experiencing a difference in mileage or noises from the pipes...the only thing that is wrong with the pipes at this point is one of the welds is broken on the passenger side where the pipe is welded to the rod...I don't think that has anything to do with it...BUT I'd like to hear from you guys...what do you make of all this?

 

If you have broken or cracked welds then this could be your issue as it is leaking and allowing fresh air to get in the pipe and mix with exhaust. The O2 is detecting that and giving the code. Also check all the manifold bolts on both sides of the engine for those to be broken or loose

 

Yeah, much as I hate to agree with 'Weed (it gives him a big head, LOL) it's entirely possible the cold fresh air mixing with the exhaust gases is your issue...

 

P0420? Sounds like your truck is smoking too much... It might be stoned

 

It really pisses me off that the weld broke on me...I got it done from a friend of my dads and he only charged me 200 bucks...they are the equivalent to Flowmaster, but are not the flowmaster brand name...not sure the manufacturer on them...he did the job super quick and I noticed on the weld that there was a lot of porosity...the guy just didn't take his time on it and I regret it now...so I should get the weld fixed and see if that fixes it then?

 

I had this problem Code as well. Small pin hole on top front of my Cat just aft of the sensor where my Flow-Tech Y-pipe went in, Re-welded and I was golden.

 

Make sure the metal is wire brushed good or grinded slightly and clean to get the best welds. Especially if using a MIG.

 

I gave my Grandpa a call a couple days ago and was asking him about the P0420 problem and he says to go buy a can of Gumout Carb Cleaner and spray it across the hoses and what not and the engine will come down a bit I guess. He didn't really get too much into detail with it since I orginally didn't call him for that reason...BUT he said his CEL came on for a O2 sensor problem and he did the Carb cleaner trick and he said it worked and never had the problem again...I'm wondering what you guys think of that?

 

Spraying carb cleaner accross the hoses is to detect a vacuum leak. it hasn't anything to do with an exhaust leak or a bad 02 sensor. If a 02sensor gets dirty, it can throw out false codes just the same as if the sensor is going or is bad. You can easily check the voltage output and resistance of the 02sensors using a multimeter.
They should be replaced at or before the 100kmi mark for preventative maintenance anyways as they are only design to last that long to begin with!

 

Alright...heres an update...I haven't got to fixing the O2 sensor yet...BUT...I did a little bit of playing around and decided to disconnect the bettery and let the computer restart...I drove more than a day without the CEL ever coming on...SO...Heres my next big question...could the O2 sensor really be ok and it just be the small hole in the rear of my exhaust where the bracket broke loose (where it holds the pipe up) from that bad weld and it's throwing a false code?