02 sensors are not the cause for most lean bank issues. Could be the MAF starting to fail, but if it is dob't try and clean it, that will just assure you that you will get to buy a new MAF, they don't take to being cleaned. To be a MAF failure you would also need to have a 4th. gear out of ratio fault showing as well.
Exhaust leaks, vacuum leaks any number of things will throw lean codes

 

Mike,

I just had my truck throw the two codes today....
P0171-System too lean (Bank1)
P0174-System too lean (Bank2)
If what I am gathering from this thread...theres not much I can do until I start throwing other codes as well...is that correct? I currently have 88086 miles on the truck. Any further insight would be greatly appreciated!

 

Just to be sure, make sure you have the o-ring that fits in the MAF sensor housing, just before the sensor. It's a big 1/4" thick, 3" ring, you can't miss it. Unfortunately, I did and I was getting all 3 codes off and on for months (mostly the 4th gear ratio). I replaced the ring a few days ago and no codes so far, but time will tell. Of course, this morning I found my old ring when I was cleaningthe garage, I'm guessing it fell out when Ihadreplaced my air filter [sm=headbang.gif].

Also, Iwas getting lean codes and the 4th gear code when my crank sensorfailed and the truck died.It seemspossible that my sensor has slowly been dying and throwing those codes intermittently if the engine were to momentarily quit while driving.