Why would a new spark plug cause a check engine light to turn on?
I bought a 1997 Honda Accord four days ago. The next day a sparkplug broke. Yesterday I brought it into the mechanic and he replaced the plug. I noticed on the way home that the check engine light came on. I know nothing about cars, so I figured it needed to cool down or something. However, today it was still on and the engine seems louder than I remember it (though this could be my imagination).
Any idea what this could be, how much it would cost to repair, and how severe it is? Meaning can it wait til the weekend so I don't have to miss any more work (the mechanic is closed by the time I get out).