On our cars the cat codes are often really phantom codes. The pre-cats are the only cats that those codes apply to on our cars. Try catching up on maintenance, then turn off the light and drive it for a while to see if the code comes back. You may have nothing to worry about.
My car is one of the many that has the cat code show up ocassionally but further testing reveals that the pre-cats are functioning fine. It has always passed a dyno loaded smog test with flying colors.
By catching up on maintenance, I mean oil and oil filter, air filter, clean throttle body, and run some injector cleaner through the fuel tank.
If there is any doubt about the upstream oxygen sensor for the bank involved, change it.
Those codes are set when the downstream oxygen sensor too closely matches the upstream sensor. If the upstream sensor is lazy it can contribute to the code getting set.
Also, there is a Ford TSB for many of the 96 to 97 (and I think even some 98) models that provides a new program for the PCM that widens the parameters for setting the codes. It may be worth talking to your Ford dealer to see if your car is one of them and how much the reprogramming will cost.
