2006 Tribute 4 Cylinder Throwing 420 Code

I've had my Tribute for about 3.5 years in which I've put 110,000 miles on it, and the check engine light is on, and the code it's throwing is 420 which reads "catalyst efficiency monitor malfunction - bank 1". The general consensus on this is that the warm up cat on the exhaust manifold is no longer doing it's job, but I wanted to get opinions from anyone who has dealt with this issue. Any helpful input would be appreciated, thanks..