I have a 2002 Dodge Intrepid. Friday night the check engine light came on when I stopped at a red light. When I got home I checked the code and it was P0138. I drove it for a couple of errands on Saturday and the light came on and stayed on every time I drove it. However, the check engine light has not come on since Saturday. The car drives fine and appears to have no obvious problems.

All I know is this has something to do with the oxygen sensor and voltage. Is this a problem that could have corrected itself or should I have the car checked out?

It must have been a one-time out of tolerance fault. After around 40 engine cycles, it the malfunction hasn't reoccured, the light will go out and the code will erase (that is unless you reset the code prior). Anyway, if it tripped once, it will probally trip again in the future. Just keep an eye on it and change it when it's a harder fail.