Pontiac Repair: engine service soon light came on, pontiac grand prix, oxygen sensor

Question
is it the altanator , spark plugs or oxygen sensor( 1999 PONTIAC GRAND PRIX GTP )

Answer
best thing to do is take it to a mechanic and have them check it with a code reader.this will explain the reason for the light.you can also go to autozone and they will check the codes for free.or if youre a do it yourselfer you can purchase a code reader for a couple hundred dollars.i would recommend having it fixed by a reputable mechanic.if the car is running bad i would recommend having it fixed asap.problem could lead to engine damage.