Everyone that owns a newer vehicle should own a Diagnostic Reader. They aren't that much money and they are very handy. As mentioned before, you read the codes and look them up on the internet. Usually it is a sensor that can be replaced fairly easily and they save you a ton of money in the long run.

Codes can also be erased by removing the negative battery cable for about 10 minutes. Since the code comes on and goes off intermitantly, it could be anything and without pulling the codes you won't know where to start. Very often a light that goes on and off indicates a misfire condition and a simple set of spark plugs will solve the problem.