My check engine keeps coming on and off. Today I took it to Autozone and they gave me error codes P0420 and P0141. I put a new CAT on about 10 months ago, Could it be my secondary o2 sensor thats going bad? I need to take an emission test soon so I need to fix this as soon as I can. Thanks for your help. BTW its a 2001 Accord 4 cyl.

 

Was your new Catalytic Converter OEM or aftermarket? There is a very good reason why factory Catalytic Coverters cost more.

 

Try drilling a spark plug non fouler and putting the o2 sensor in that, and that into your cat. If the cat flows to much you'll throw a code ( happens with test pipes) but if you back the plug out a little it'l get less flow and hopefully balance it out.
This is assuming of course that your new cat doesn't meet oem spec.