Hi

Got a check engine light on tonight, I did the pedal pump test and got back code 1222 which is lambda control 1. I understand this is probably the o2 sensor but which one? A while ago, I took my car to the stealership with a check engine light and they diagnosed a faulty o2 sensor (didn't tell me front or back) as I was driving home the engine light went off. It came back on today with that code. I plan on fixing it myself but need to know whether it's the front or back o2.
If anyone can help, it's appreciated.
Thanks
Nate