I have a 1992 Ford F150.Before I changed the spark plugs the check engine light was not on.
after the new were installed,light is on and does not flicker.could this be the oxygen sensor?

 

First thing that can to mind since the CEL wasn't on before,, was that the small plastic colored vacuum lines that run to the vacuum reservoir and top side on over ect. like to break with age or if disturbed.. Iv'e broken more than a few trying to work around them.. A vacuum bleed will cause a low read in the O2.. If the engine doesn't have any performance issues, look around the area of your work..

 

How would I know if this is my problem? Where are these hoses? WHere is the vacuum reservoir, and what does it look like? My check engine light came on the day after I got my oil changed. The guy who changed it has noticeably shaky hands. The code is for Bank 2/Sensor 2.
2004 Freestar. The engine has zero performance issues. And my mileage hasn't suffered.

JM