You have nothing to worry about on OBD-I cars that only have 1 o2 sensor in front of the catalytic converter.

OBD-II cars usually have 2 o2 sensors. If you have a 2-sensor o2 setup, then it (could) make it come on if your setup doesn't heat up the catalysts enough for them to "light-off". The front one is what your ECU uses to regulate the fuel trim. The one behind the cat is there ONLY to determine if your cat is working. So if you throw a code for that thing, the CEL means nothing about your engine's performance.

In fact, the rear one isn't even very sensitive. A friend of mine gutted his cat on a OBD-II turbo eclipse, and never threw a code for it. There is a hack to disable that thing using a 1 microfarad capacitor. :thumbup:

http://www.thefbody.com/~95tsiawd/O2bypass.html