need o2 sensor help

new to this site so i dont know if this has been asked before. i have an 01 f250, 5.4 and check engine light came on. codes were 171 and 174. put new MAF sensor in and now only code showing is 171. parts place then sold me a front o2 sensor. ive read in my haynes repair book that theres an o2 sensor on the exhaust man. and one behind the cat. converter. unless im just seeing things, or im totally stupid, i see two sensors up front. one on each side of the engine. i see nothing behind the cat. so my question is, where does this front o2 sensor go? plus, the pigtail on the sensor napa sold me is way shorter than the pigtail on the two sensors i see. HELP!!!!!!!!!!!!!

you will have an o2 senor for each bank but you should have one after the cat that one is to determine cat efficiency the code will tell you witch bank is bad they should have asked you how long you needed the pig tail to be

thaks mike, i assumed the pigtail would be right when they told me there was only one option for the front. the code says its bank one. so im trying to figure out where this sensor goes. if it is the right sensor, where is bank 1?

you will have an o2 senor for each bank but you should have one after the cat that one is to determine cat efficiency the code will tell you witch bank is bad they should have asked you how long you needed the pig tail to be
bank one is the left side as you are sitting in the truck

appreciate the info