95 Neon Check Engine (Code 12,Code 21)

My 95 Neon Check Engine light came up last week. The car sees to run fine. I read somewhere that this combination of codes is the result of sum hickup and should clear itself if it is a false code. Anyone else experience this? I'm going to reset the codes and see if it comes back. Where are the oxygen sensors located? How accessable are they? Can I test them somehow without any specialize tool?

Corey

the o2 sensors are located as follows: the upstream is on the exhaust manifold right behind the motor, the downstream is right after the cat. converter. its highly recomended that you buy an o2 sensor socket, available at auto parts stores for around 15 dollars