Mitsubishi Repair: service engine soon light, spark plug wires, mitsubishi mirage

Question
I have a 2001 mitsubishi mirage de and the other day my service enginge soon light came on so I took it to my mechanic barely it was stauling on me shaking and doing other things and he told me it was my spark plugs and we replaced them and the light went off. Today when I started to drive it came back on and to me my car seems to be running better than I can remember do you have any idea what could be wrong so I can fix it and not keep paying the mechanic?

Answer
Jackie,
Many times when your car's computer detects a spark plug does not fire properly (even if only once), that will cause your check engine light to come on and stay on.  You mentioned your mechanic replaced your spark plugs.  He should have also replaced your spark plug wires, distributor cap and rotor.  Have those items replaced as well if they weren't replaced with your spark plugs.

Also, if you have an Auto Zone in your area, you can take your car there and they can scan your car's computer for free, and inform you why the check engine light came on again.  That should help pinpoint the cause.  Your light may have come back on for an emmissions issue.
Good luck!