Originally Posted by waterbug
Why only one spark plug? Not that it matters. Was there a problem with it? Did you gap the spark plug properly?
I believe the check engine light can mean there is an error code related to your emissions system (oxygen sensors). This might be related to your spark plug, as it may not be firing properly and putting too much unburned fuel in your exhaust stream.
Its very possible it may just be a misfire code. the only way to go about this is to get the actuall code. We can guess all day but why be wrong when we can be right.