Do you know what the code was BEFORE the repairs? If not, how are you going to know if the problem you have now is the same. Anybody who offers a guess as to why your light is on now is somebody that knows nothing about modern vehicles. There are over 2,000 possible trouble codes that can set off a check engine light. That's why you can't guess at what's wrong. Get the codes read and then you'll know.

I keep hearing people say "it's probably the O2 sensor", but have never seen one fail. Like stpaulguy said, have the codes read. Places like Napa and most car dealers will do it for free. Code readers are very inexpensive now too. I have one and it has paid for itself by not needlessly buying O2 sensors. Oh yea, coffee down the heater vents will not cause a check engine light.

Disconnect your negative battery post wait 60 seconds and reconnect it. If that don't work.Then it might be your o2 sensor.and if your light come back on then most likely it's your o2 sensor. Do your car run kinda sluggish ?

It's most likely the oscillation adjustment screw relay control valve solenoid bendix sensor

Just had my ignition switch, spark plugs, and some other stuff replaced. Before I got my car fixed my check engine light was on, (Not flashing). When I was pulling into my driveway I noticed that it was on again. I got coffee on the way home and a bit spilled into the AC/heater fan part of my car but I don't know if that would be enough to cause it or what?