We have a 97 Sunfire 2.2L. Just a few days ago, it started overheating. The cooling fan will not work when the engine is at operating temp or above. It works when the engine is cold with the AC turned on but after warming up, even the AC being on won't make the fan go. It is not the fuse or relay, I have checked. The fan works fine when jumped. It seems to be somewhere between the relay and PCM or the PCM itself. It isn't the Coolant Temp Sensor because it would still run with with the AC on if that was the problem. I don't want to bypass and add a switch unless I just can't fix the problem. Has anyone who has had this problem figured it out? It seems to be a common problem.

Anyone? This problem seems to be common. Has anyone figured out what causes it?

Check all of the electricals between the fan, switch, relay, AC switch, etc. for proper operation and voltage/ground continuity and against shorts. It may help if you draw a quick diagram to use as a checklist. A factory service manual would be your best friend. It's one of the first thing I buy for any of my cars, and probably the best investment you can make if you plan on fixing anything yourself