[Angel1]

The SES light is came on in my 335i, (61,000mi) it was due for oil change so just took it in. Dealer told me they couldn't find the problem, asked if we'd put performance enhancing product in it - which we haven't. They reset the SES and sure enough two days later, it's back on. Had AutoZone read the codes and they say it's MAF but thought I'd get more info. I've read several posts and sounds like the MAF can be cleaned but I'd need some really specific instructions, please help!!! Love my car, but dealer service prices killing me!

[boom]

N54 335s don't have MAF sensors. They run on speed density calculated by the MAP sensor and the intake manifold volume. Fueling is controlled in real time by the first wideband sensors in the downpipes. It is checked by the second wideband sensors. If you're throwing lean codes then either your car is not calculating the right amount of air (MAP sensor) or your widebands are screwed up or your injectors are clogged and not injecting enough fuel. I would imagine that because both banks are lean, you're on stock boost, and have never messed with the downpipes you need a new intake manifold MAP sensor. If that doesn't work, get new widebands.
You can test all of this with an OBDII scan tool that reads real time values. CHeck the MAP sensor function and the wideband values. These may be hard to find b/c BMW uses specific PIDs and scan tools can't read everything. The best tool for this would be the Bavarian Technic but it's $300 and requires a laptop.

[Angel1]

Thanks for the information, I'll see what I can figure out.

[utfenix335i]

Sounds like what happened with my car after my catless downpipes were installed. I would check your o2 sensor.

[GRLPWR]

Originally Posted by boom

N54 335s don't have MAF sensors. They run on speed density calculated by the MAP sensor and the intake manifold volume. Fueling is controlled in real time by the first wideband sensors in the downpipes. It is checked by the second wideband sensors. If you're throwing lean codes then either your car is not calculating the right amount of air (MAP sensor) or your widebands are screwed up or your injectors are clogged and not injecting enough fuel. I would imagine that because both banks are lean, you're on stock boost, and have never messed with the downpipes you need a new intake manifold MAP sensor. If that doesn't work, get new widebands.
You can test all of this with an OBDII scan tool that reads real time values. CHeck the MAP sensor function and the wideband values. These may be hard to find b/c BMW uses specific PIDs and scan tools can't read everything. The best tool for this would be the Bavarian Technic but it's $300 and requires a laptop.

Great explanation (I couldn't figure out if I had MAF/MAP sensor). I'm getting post cat fuel trim system too lean and o2 sensor signal stuck lean bank 1 sensor 2 codes. Car runs fine otherwise, but when the SES comes on, you can feel a slight miss. Car is tuned, catless dps, dci. I've had 1 pre-cat sensor replaced, both swapped, but nothing done to the post-cat sensors. Any comments/suggestions? I don't have a BT tool, but I do have a generic scanner (getting codes P2270 and P2096). Someone suggested o2 sensors spacers (???) and I've tried cleaning/swapping the vanos solenoids.

[utfenix335i]

I think your O2 sensors are bad. change them

[boom]

+1
I think your bank 1 sensor needs replacing.

[GRLPWR]

Originally Posted by utfenix335i

I think your O2 sensors are bad. change them

Fair enough. Thx. Would that be pre or post? And, is it true the post cat sensors are the more expensive, non-bosch brand? I went in for a free diag clinic a while ago and the SA said they don't use the same kind of sensors for post as they do pre's. Supposedly it's a $400+ brand (don't remember the name). I've seen a thread on what to use, but after reading it, I was left w/a 50/50 toss up as to which kind to use.

[GRLPWR]

Originally Posted by boom

+1
I think your bank 1 sensor needs replacing.

Ha! Guess we hit the 'submit' button at the same time. I was hoping you'd chime in. So, bank 1 - pre cat? Still learning.....

[utfenix335i]

I believe it is pre cat.