i have a 2003 bonni. ssei and my check engine-light came on a month and a half ago. i took to autozone a two weeks later (which was a month ago),they told me it was my o2 sensor the one before the cat.convertor so i got it fixed that same day and now its coming back on and autozones scanners are saying its my o2 sensor the same one i had fixed.

If you bought it at Autozone, it was a Bosch O2 sensor, and they simply don't last in our cars. AC/Delco or Denso are the only ones proven to hold up.

Have you been getting into the pedal any; firing up the boost?

everytime I'm in boost I can count on an O2 sensor code flashing the check-engine light. After a few trips of normal (non-boost) driving the code clears and the light goes out. Not sure what'* causing it, but for me at least it'* consistent.

So I'd drive it as is for a few days, see if it goes away on it'* own. If not, take it back and get a new sensor, maybe you got a bad one.

SAMKIVEL
What is the code that their scanner is showing?(this will get better help from gear heads) I would guess it says something to the effect of "lean bank 1". when the scan tool pointed at the bank one sensor that meant that sensor saw a problem or possibly was the problem. If you changed the sensor dont go buy another one until you rule out the following.
1. fuel pressure (you might not have enough and your really running lean)
2. vacuum leaks (will also cause a lean situation)
3.clean battery terminals (this can and has caused the same problem for members here)

As stated above people here don't like Bosch sensors because they fail early, a simple scan tool can tell if the sensor is bad by the rate the voltage toggles. I wouldn't replace it until you know it'* bad.

Dang it SJ.. you beat me to it.

If it'* the P0171 Lean bank one code...it'* rarely a sensor.