well you have OBD2, it could be something simple like an oxygen sensor too. like they said, you can get the code yourself if you can get to the ECU. all you should need is a screwdriver. if it's easier, autozone should be able to plug in and tell you what code it's storing. I got an EGR code when I got my 94 sentra last year, but I was able to clean out the intake and everything and that cleared it up. those code scanners aren't 100% accurate because sometimes, one code can spawn another. a common example is a misfire can cause a lean condition, causing a false reading on your o2 sensor. you'd be throwing a misfire and an o2 sensor code. when was the last tune up?