I have a reader as well and I live downtown for the most part if that is closer for you. If it doesn't come back then it sounds like the PO may not have cleared the codes after replacing the O2's but most likely not the same. It will come back after so many miles. I think it is like a 3 trigger component meaning that the event needs to register 3 times prior the light coming on so you may already have a stored code.
97 Crusher, Slee'd 6 inches, All 3 Factory Diff locks, Hanna Sliders, Slee F&R Rock Crushers, M12000 Oops, I did it again saver -- SuperCharged.......0-60 in 5 seconds,
"Tractor in a Tux"
What Did the Five Fingers Say to the Face.....