I did a search, really couldn't find an answer, so here's the question: A friend's 2001 F150 with the 4.2 popped up the P0171 code the other day. The reader said it was the P/S bank, so with 130,000 miles, and a recently-replaced D/S O2 sensor, we took the advice of the guy at the shop and replaced the P/S O2 sensor in the manifold and reset the light. It was fine for a few days, but the CEL came back on, and after another visit to have the codes read, same code, but now showing on both banks. I didn't realize that there were 2 more O2 sensors in the cats, but before we replace those, does it sound like that could fix it? I check the MAF, thinking it might need cleaning, but it looked clean, as was the inside of the intake. I'm really hesitant to mess with the MAF given it's fragile nature, if it did need to be cleaned, would that be something visible to the naked eye, or are those things so sensitive that tiny particles would foul it?

So, aside from the O2 sensors and the MAF, is there anything else that could set that code?

Thanks!

 

my dad's does the same thing, we replaced both O2 sensors, fine for a few days, came back on.........He has an intake gasket leak.

might look for that, vacume leak would cause it to run lean

DT

 

I had the same problem with mine it was a vaccum leak in the two rubber elbows for the intake and the pvc valve. The one is very tricky to get to because it is at the back of the intake.

 

Well, it's been a while, and after resetting the CEL, it hasn't reared its ugly head... hopefully it stays that way for a while. I will certainly keep in mind vacuum leaks when/if this issue needs to be revisited. (it's a Ford, I'm sure it will!)

Thanks for the replies thus far...

-IKE