so i was driving down the road and my CEL came on i stopped at advanced auto parts to have a scan and it gave me this

P1131
Insuff. Switching
02 Bank 1 Sensor 1
Sensor/Lean

i don't know which o2 sensor this is i was told its the one before the converter but i am clueless as to what side its on

also on the way home about driving about an hour with the CEL on it decides to go off

any input is helpful please

 

can someone tell me which side this is talking about passenger or driver?