Lean codes bank 1 and 2

[Gastiboi]

Having a headache for months trying to
figure out the lean codes on my 2002 E39 wagon.
P0171 and P0174. Did replace the CCV,valve cover gasket, valve cover
No leaks from the smoke test, no loss of power. Don’t know what else to do.

[E39 Newbie]

Sometimes a flakey MAF will cause lean conditions, especially if they show up in both banks.

[Jaaap]

Check the fuel pressure.
If it is ok, check how fast it can recover to the correct pressure when you let the pressure off.

[Chedley]

That ^^
Also replace the fuel filter/ regulator if you have never done it on this car

[R Shaffner]

On these cars you have to smoke test the crankcase too. A leak there can cause unmetered air to enter the intake through the PCV system.

[TiesTorN]

your cats are probably clogged.

[Colby White]

I also has this same issue for months if not longer. Then I started to pop my transmission fuse. That was just another issue in a series if issues. However, I discovered my transmission fuse is linked to O2 sensors. So I checked around them again and traced the wiring in its protective jacket behind the block, (where I could only feel instead of see) I ran my hands down one of the O2 sensors wiring. Something felt awfully wrong back there. I fished out and found about 10 inches of wire that was fused together due to heat (and probably age) My e39 is a 2001. The wire was so bad, stiff as if it was a piece of iron and cracked exposing bare wire, clearly causing issues with my O2 and now popping my Transmission fuse. After cutting out the damaged wire and splicing the ends together, my transmission issues solved, O2 issues with bank 1 and 2 showing lean also solved, and so on. Check your wiring....

[oldmangrimes]

I had the same codes, replaced the usual suspects like you did thinking it was a vacuum leak, etc. This time my valve cover was leaking oil, so it had to be replaced anyway, but I still got the codes after replacing it. I had occasional rough cold starts, too, so I cleaned my ICV and throttle body (They may never have been cleaned in 195k miles, they were both dirty). Codes haven't come back, and it's been a few hundred miles and many starts. It didn't cost me anything to clean them, just the time and hassle of getting to them. I could imagine how if one or both were sticking then it would cause the wrong amount of air to get to the engine and cause lean codes. The car idles better on cold starts, and seems to accelerate smoother.