Hmm, possible revision to my answer earlier. My car's check engine light came on while on my way home from work. Now, two problems in 42K miles isn't necessarily bad, and it is still under warranty (it is a Hyundai). However, depending upon what it is I may just be in the market for a new car. You see, the one prior problem (some kind of emissions issue) started with the check engine light. After my last car (a 1997 Nissan Sentra) went through about a dozen alternators I promised myself to get rid of any car that showed signs that it would have the same recurrent problem, and if this is the same problem as last time I may have to honor that promise to myself.
So, unless this problem is something else, I may just save the tax return in order to buy a new car (well, probably a used car) in the next few months. The return will be just big enough to use as a down payment (man I hate the idea of selling my car when my loan is higher than the used car value though).