Toyota Repair: Error code using Autozones analyzer, 2006 toyota corolla, o2 sensors

Question
Hello,
  I went to Autozone today because I had a check engine light on. The guy at Autozone used his engine analyzer, and he come up with a code that read like this: PO171 system to lean bank1. He said, "That usally means a O2 sensor" Well my 2006 Toyota Corolla has two O2 sensors before and after the catalytic converter unfortunately it don't say which one is bad. Would you be able to advise me as to which one I need to replace


Answer
You don't need to replace them, remove them and clean them.
The computer is saying the vehicle is running a little rich or lean.
IT DOES NOT mean the sensor(s) are bad. Auto parts stores just want to sell you products. If I received a dollar every time a 02 sensor was replaced on a vehicle I'd have millions. Those guys are not technicians! A really good expensive scanner will tell you what's causing it. If the vehicle has over 60K
miles change the gas cap! Toyota recommends changing the gas cap every 60K miles.