Chevrolet: service engine soon ligh, chevy lumina, oxygen sensor

Question
my chevy lumina was driven 1900 miles in the last 3 days with the last day being in california.gas was purchased in california the last time.  the next day on starting the car the service engine soon light came onsteady.  the handbook says to ck the gas cap and if fuel was purchased that was different to refuel and run for several trips. as the problem could be with the fuel or filler cap.  or in the emission system. the fuel m ilage dropped with the last tankfor about 2 miles per gallon.  what could be the most probable cause--catalytic converter or some other part of the emission system.   the auto is a 1996 lumina ls/3.1 engine with 94000 miles.  no previous problems.

Answer
Hi Jim, the most probable cause for the light is the oxygen sensor. The oxygen sonsor should be changed as regular maintenence, your car has 94000 miles its well in need of replacment. Take your car to a shop and have it hooked up to a anylizer this will tell you exactly why the light is on. I hope this helps you . Regards, Keith.