I have a 2004 Infiniti G35 and the bank 2 catalytic converter has triggered the check engine light. If I replace it with a universal Magnaflow catalytic converter (approximately $100) will the check engine light come back on? According to the mechanic who diagnosed it, the existing cat is CA compliant. The universal cat is 49 state compliant, no CA. I live in CO. Also, Magnaflow has an exact cat replacement (approximately $600) which is also only 49 state compliant. I asked around a few mechanics and didn't get a good answer. I just don't wanna replace it and still have the check engine light on, since that will automatically fail the emissions in CO.
Newer cars (1996 and later) have additional catalyst agents than the old cars had. $100 sounds like one of the old car cats. $500-1000 is more in the ballpark where the newer cats are typically found. Will an old cat keep your light off? Perhaps. Perhaps not. Is it a legal replacement, no, not from what I remember of the federal code.
What's the return policy? If it doesn't work, can you get a refund? If so, you might give it a shot, if you're not paying anybody to put it on. If you are, shop around for the cheapest estimate where they'll guarantee the repair. You don't want to pay for labor to find out the cheap cat doesn't work. A factory part should be guaranteed to work, but that will probably give you sticker shock unless you can get it wholesale.
Before you start messing with replacing the cat, are you sure your O2 sensors are good? Did the mechanic scope them? If it was me doing driveway diagnostics, I'd be tempted to swap O2 sensors between banks and make sure the fault didn't hop to the other bank.