Hopefully new sensors fix your issue. There is a lot that goes into properly diagnosing them; you (or somebody competent and capable and with the scanning equipment capable of doing so) need to view several live data parameters - short and long term fuel trims, sensor voltage, MAF sensor values, fuel pressure..... The list goes on. And then also check for other things such as vacuum leak/unmetered air being drawn in, wiring issues, and pretty rare but you can also add faulty PCM to that list.
At this point you are doing your best to make an educated guess. So like I said, hopefully this fixes it. These sensors do go bad, but more often than not they are just doing their job (reporting a lean condition, in your case) and the source of the problem lies elsewhere. The P1151 (not switching) code could definitely be further evidence of a faulty sensor (your P0171/P0174 codes generally are not indicative of a faulty O2 sensor), but essentially what the "not switching" portion of the code description means is that the a/f ratio is so far out of whack that the PCM cannot add or subtract fuel as necessary to correct the condition. Being that you have both banks reporting a lean condition, it's not impossible but I find it hard to believe that both sensors took a crap at the same time.
Anyway, R&R is not too difficult. Except that passenger side, which looks like you've already discovered. If you cannot fit your hand/arm between the floor pan sheet metal and catalytic converter to get to the connector, you may try accessing it from above the engine instead. Either way it is at least slightly difficult and definitely a little cramped as far as space to get your hand in there goes but you should be able to get to it. I hate dealing with that side as well, far from impossible but it's legitimately kind of a b!tch - especially if the little clip that holds the connector to the engine is broken (like on my car, lol) and then you have to make your one hand that can fit in there and reach anything do the job of two hands to hold and line up both connectors and then snap them together. Fun stuff indeed.
And hopefully you aren't trying to remove and install with a regular open-end wrench or crescent wrench. Those can be used, but you'll save yourself a little bit of headache and some cussing if you invest in an O2 sensor wrench or socket to go on your ratchet (yes, they make a specific tool just for these things, and they do make the job a bit easier).
As far as part numbers, it is probably due to them being listed as left or right side specific. It honestly does not matter though, which sensor you place on which side. A common trick used to diagnose a bad sensor when only one bank is reporting lean or rich condition is to swap the sensors and then see if the problem switches over to the other side of the engine - which further proves that left/right orientation and part number don't matter. Some vehicles use sensors that have different pigtail lengths (not applicable to our cars though), so that is why it is common to see specific part numbers for left and right. The sensor itself is identical though.
Good luck and let us know how it goes. Be sure to disconnect the battery "-" terminal while you're working; this will reset the PCM fault codes and also allow it to re-learn air/fuel trim values when you get it all back together.
At this point you are doing your best to make an educated guess. So like I said, hopefully this fixes it. These sensors do go bad, but more often than not they are just doing their job (reporting a lean condition, in your case) and the source of the problem lies elsewhere. The P1151 (not switching) code could definitely be further evidence of a faulty sensor (your P0171/P0174 codes generally are not indicative of a faulty O2 sensor), but essentially what the "not switching" portion of the code description means is that the a/f ratio is so far out of whack that the PCM cannot add or subtract fuel as necessary to correct the condition. Being that you have both banks reporting a lean condition, it's not impossible but I find it hard to believe that both sensors took a crap at the same time.
Anyway, R&R is not too difficult. Except that passenger side, which looks like you've already discovered. If you cannot fit your hand/arm between the floor pan sheet metal and catalytic converter to get to the connector, you may try accessing it from above the engine instead. Either way it is at least slightly difficult and definitely a little cramped as far as space to get your hand in there goes but you should be able to get to it. I hate dealing with that side as well, far from impossible but it's legitimately kind of a b!tch - especially if the little clip that holds the connector to the engine is broken (like on my car, lol) and then you have to make your one hand that can fit in there and reach anything do the job of two hands to hold and line up both connectors and then snap them together. Fun stuff indeed.
And hopefully you aren't trying to remove and install with a regular open-end wrench or crescent wrench. Those can be used, but you'll save yourself a little bit of headache and some cussing if you invest in an O2 sensor wrench or socket to go on your ratchet (yes, they make a specific tool just for these things, and they do make the job a bit easier).
As far as part numbers, it is probably due to them being listed as left or right side specific. It honestly does not matter though, which sensor you place on which side. A common trick used to diagnose a bad sensor when only one bank is reporting lean or rich condition is to swap the sensors and then see if the problem switches over to the other side of the engine - which further proves that left/right orientation and part number don't matter. Some vehicles use sensors that have different pigtail lengths (not applicable to our cars though), so that is why it is common to see specific part numbers for left and right. The sensor itself is identical though.
Good luck and let us know how it goes. Be sure to disconnect the battery "-" terminal while you're working; this will reset the PCM fault codes and also allow it to re-learn air/fuel trim values when you get it all back together.
