1994 Toyota Paseo check engine light

Engine Mechanical problem
1994 Toyota Paseo 4 cyl Front Wheel Drive Automatic 155k miles

I just had an o2 sensor and a fuel filter put on my car because my check engine light would come on and off and then finally stayed on. I almost made it home tonight and the check engine light came back on. What can it be. I cannot find a shop that will scan it for the code.