I got a P0420 cel the other day and I cleared it then I just drove it again today for the first time since clearing the light and it didn't come back on.

I have a Magnaflow cat that is a couple years old, a glass pack and no plenum gasket so i can't leak oil into the cat.

I'm thinking it's either a fluke from the higher flowing cat, an exhaust leak, the fact that it was raining like crazy that day or maybe I'm running a little rich and the cat really is inefficient like the light told me.

Any thoughts?

 

Did you replace the sensor when you replaced the cat?

 

I reported this a long time ago. The old recommended magnaflow cat didn't work for me. Threw a cel 6 months later. Aim recommended a heavy metal magnaflow. I chopped the old exhaust back out, installed everything new. 6 months later, the heavy metal cat started popping an 0420 as well... At that point I was furious after spending that much for nothing. I tossed a non-fouler on and never looked back.

Edit - I dug up my old thread. Jan 2010 (4 months shy of 2 years).

https://dodgeforum.com/forum/2nd-gen...-surprise.html

 

I replaced the upstream but I didn't replace the downstream. Two days driving and it hasn't come back yet. I think it might have gotten some moisture in the pigtail and screwed with the voltage a little since it was raining so hard that day. So I'll put some dielectric grease in the plug and if it comes back again then I'll do the non fouler thing.
My Magnaflow is the universal one that cost around $70.

 

Sounds good, good luck!

 

Wow, sorry to hear the HD cat didn't work for you, pc. Worked great for me, but I guess your pcm is a but more temperamental.

 

No problem at all Aim.... (except for that check engine light every now and then :P) jk! It wasn't on all the time, just random occurrences. The non fouler fixed that completely. In all seriousness like I said it was frustrating looking back after replacing the cat to "do it right" for state inspection, only to have the same problem... when I could have just put the non fouler in the first time and been at the same spot without the extra expense and hassle. I chalked it up as a learning experience and moved on . I still do think your cat recommendation might help others, but like you said mine is just more "special" for some reason lol. Really though, no apology necessary. I've always appreciated your responses on here