Personally I would clear it and wait for it to come back. I've had fluke p0420's before. You can also check the temp of the cat (I can't remember what it should be) with a laser temp gauge and/or borrow someone's scan tool to look at you O2 sweep.
"-1988 Red Hilux Standard frame, X-tra cab, locked F&R, 5.29's, 35" tires and a SAS. In Moab
"-1988 Hilux, 1999 3.4L, Supercharged, 2.1" URD pulley, URD 7th injector, 2 1/2" Magnaflow exhaust, TO DO: lift, locker.
"-1987 Super Beast
"Did you know the IFS was designed by Hitler himself to make the life of 4WD owners tough? Yeah, it's true, he saw a vision of the Devil and he told him to do it." -DaveInDenver