Need HELP!

**Teknik_SS** · 04-21-2009, 10:25 AM

I got a 01 SS with the LS1 and I put MAC long tube headers on it and I have been running no cats for the past 2 years. I have had o2 sims, Well I was tired of stressing out about utah emissions so I decided to slap some magnaflow high flow cats on. Well It ran good for about 600 miles then the check engine light came on.. It was code po420, I looked it up and it was something to do with my bank 1 cat. Well I cleared it and did the drive cycle. Light comes back on... I have cleared the code 4 or 5 times. light still comes on.. So I took it to the dealer and they said that the cats are to small?!?! I thought a cat was a cat as long as it cleans the exhaust??? I got them from a muffler shop and they are ok for OBD2. Any help??

**Hi-Po** · 04-21-2009, 11:03 AM

0420 is catalyst system low efficiency.

Seems your new high flow cats dont quite to the same job as OEM cats.

**Teknik_SS** · 04-21-2009, 09:12 PM

Well I am hoping that maybe I just got a bad cat!? It is under warrenty so they are replacing it. Does anyone else have any problems with aftermarket cats?

**BlackSS1** · 04-22-2009, 03:11 AM

Yes when my brand new hiflow cats went on with the headers, the SES light came on, same thing. They are too small like HiPo says, you will need to get a tune to fix the issue.