Check engine light on 2003 toyota tacoma, O2 sensor?

An O2 sensor code is a tricky one. It could mean SEVERAL different things, and I know how bad it sucks to hear this, but your best bet is to take it in and have a diagnostic ran on it at either a dealer or a good mechanic shop with a computer they can hook up to it. I had an "O2" code come up a while back on another car I used to have, and literally spent weeks and hundreds of dollars trying to fix it, and never did. Finally out of desperation took it in, paid the $90, and they found the problem and fixed it in like 30 minutes. Something I would have never even thought of was causing it (can't remember off the top of my head). After that I stopped wating time and money on check engine lights. One comes on in my car, I take it to have it ran for free at and auto parts store just to make sure it's not a loose gas cap or something, just to get an idea of what I'm looking at, then go and make an appointment to have to hooked up to a diagnostic computer to track down the problem. Good luck, and hope this helps save you some time and money.

We replace both of ours Took a few hours but it worked.. We used the Haynes book for help to locate the sensors.