2002 Ford Station Wagon

Engine Performance problem
2002 Ford Station Wagon 4 cyl Two Wheel Drive Automatic 108, 00 miles

I have a 2002 ford taurus station wagon. Within the last two weeks I had my complete a/c replaced and this week the radiator hose went. Apparently the problem with the radiator hose was attached to the " heater" panel. Instead of replacing the entire panel, he bypassed the panel and connected otherwise. I don't have heater ability anymore. He also replaced a belt (sorry don't know which one) and an intake hose to the a/c. The check engine light came on within 24 hours of the radiator and belt work. Any ideas? It seems to be running okay. The gas cap was on tight but the light did come on after putting gas in the tank.
October 21, 2009.

The computer needs to be scanned to determine why the light is on. Most parts stores will do it for free. As far as bypassing the heater core, that isn't a great idea. Was the heater core leaking?