Originally Posted by 2003G35stock

Welll...I'm not sure the above it quite true. A lot of things can put a car into limp mode. Dead O2, bad cam or crank sensor are examples. Unplugging or a dead intake air sensor or a bad MAF are also possible items.

I don't know that a leak around the cat would cause it, it would more likely flash that it wasn't reading right and you would get an error.

First question is, what other errors are you getting?