Mike,
Car :Plymouth Sundance
:Automatic
:2.2 Liter
:Air Condition
:Power Steering
:Power Brakes

I just changed all fan belts & air filter on my 1991 Plymouth Sundance. It started and ran find. But the Check Engine light stays on. What could be the problem? I check all the vaccum hoses, they seem to be all connected.

You did a good job of explaining what you have. The only thing not listed was mileage. The light is programed to come on at 60,000 - 82,500 and 120,000 miles as a reminder to service certain emissions related items. To turn the light off you need a tool known as DRB II, it plugs in and with it you cancel the light.

Mike