First of all a 'check engine light' means exactly NOTHING. They can sometimes come on when the engine reaches a certain mileage target and can also come on when a sensor is malfunctioning. If doesn't really mean anything is wrong. Go to your local AutoZone or other auto parts store and they can give you a 'key' to read the error codes put out by your on-board computer. Of course you can go to a mechanic and he can check this out also.
Its good that you own a GM car. My advice if you are to own to cars is ALWAYS own the same manufacturer of car and make sure it is a model that has A - been around for a while - to insure that the defects were worked out on the newer models and hopefully have been fixed by the time your year model was produced, and B - is a high volume seller, to insure that replacement and repair parts are available and inexpensive.
Try to buy models that share the same engines, transmissions etc, such as a Buick/Pontiac/Chevy/Olds mid size cars for instance (Ford Taurus/Mercury Sable with 3.8 liter engines are bulletproof also) with a common engine - the 3.1 liter engine is a great one. This will make you familiar with common components and make you a better judge of what needs to be done if something goes wrong.
You will also be able to do light mechanical work yourself as easily on one as the other - things like oil changes, brake pad replacement, belt replacement, alternator, water pumps, things like that. Even if you have someone else do it, you will be better informed.
Go American, not just because I assume you are one. The parts are more easily available and cheaper as long as you get a high production model.
I sold my 1974 Thing last year, and that was easy, because it is a special car. But a Mazda sedan is a different story. Is there any easy way to sell such an ordinary car?