Hi was wondering if you guys can help out.

I had a tune up done a few days ago, had new plugs, wires, Distributor cap
& rotor,fuel filter, and oil changed.  I was told at that time that oil was
leaking and that I needed to have the Vale cover Gasket replaced.

Today I had the Valve cover Gasket replaced.  In addition I got the
battery terminal cleaned for the winter, and while I was added had the
engine washed with the degreaser and high pressure rinse at the car wash.

AFter driving it for maybe about an hour the Check engline light came on.
All the engine fluid levels are ok. Battery looks to be fine. no hoses
appear loose. I cant figure it out.  COuld it be the new Vale Cover
Gasket? If one of the screws were not tight closing it back up, would that
trigger it?  Not enough Silicone to seal it? any ideas?  Any suggestions?
Would appreciate your input.