Obd Code 172-bank 1 Too Rich...

Help! My 99GA SES light is on and I took it to be checked and it read code 172. What do I do to fix this problem? I have been told it could be any number of things causing it. Most said O2 Sensor. Is this correct and how do I fix it. My MPG has dropped alot since this came on.

is that only code
either faulty o2, or leaky injector, if mpg dropped i'd lean towards leaky injector.
replace o2, clean or replace injectors.

I'm not sure myself, but on my Stratus (the car I traded in for my GA) the SES came on due to cheap gas. I ran a bottle of injector cleaner through the tank, and about 3 days later, it went off. Now I always use injector cleaner about every other tank of gas. Maybe this will help you.