For the last two years I kept getting this bank 1 lean code.. well finally found the culprit and it was not the o2 sensor as many have changed.

Turns out right before the connector for the bank one upper sensor, the wires come in contact with a metal plate, and after time it rubs the wire insulation away. It there for grounds and does not send signal from the o2 sensor to the computer.. makes the engine see a faulty sensor. I covered up the bare wire and tied it up away from the metal plate. All is good.

Notes: It is very hard to get too and very hard to see so check carefully .. This was on an 03 f 250 with 5.4 v-8.

Hope this helps some of you out. I could see this being a service bulletin.

 

F250 V10, 2004. Had my oil changed and of course they had to show my the air filter. Air filter clean, oil changed and two starts later the dreaded CEL is on.
$80 on a code reader to find a P0171. Got the manual, did the research figured I would clean the MAFS. Pulled it out and low and behold, the rubber stopper around the wires to the unit had been pulled out allow a lot of air to be sucked in, after the filter. No wonder the lean code was on.