New member. First post... hopefully in the right topic. I have a 2004 F-150 with 192K miles. It has always been well maintained but it just started with these codes. I have read a lot of information on this forum regarding having both P0171 and P0172 but am looking for the most common failure point when it is just one bank. I was thinking O2 sensor but based on other posts I am no longer confident of that. Thanks for the help.