PensacolaLew

PROBLEM:

-Check engine light came on
-Ran ODBII diag
-Recieved the following:

P0174 18
P0174 System Too Lean (Bank 2)

P0171 18
P0171 System Too Lean (Bank 1)

-QUESTION:

1. Ok, four O2 sensors, pre-cat bank 1 and 2, and post-cat bank 1 and 2. Is there anyway to determine if the bank 1 and 2, in the readout above, are pre-cat or post?

2. Someone indicated that all four O2 sensors are different. I know both pre-cat sensors have a square connection and both post have a round connection. But are there really four different part numbers? And is there a way to accidently mix them up?

Thanks for any help...Lew

forlooks

Its more likely to be your MAF (Air Flow) sensor than it is your O2 sensor. I had this code and cleaned my MAF and it went away. My BMW indy suggested changing the sensor. I went ahead as a preventative maintenance. So far i've noticed better start up, better MPG, and better horsepower throughout the RPM range.

moyern83

I am having the same issue with my 2005 525i. The check engine light came on back on November 4 with 82,400 miles. I read on the forums about cleaning the MAF also, so I cleaned the sensors at that point. I cleared the codes and my CEL stayed off. I changed the spark plugs out on November 12 with 82,600 miles (same OEM Bosch plugs). The light stayed off until January 27 with 85,800 miles. I cleaned the MAF again and reset the codes...the light came back on within a week. So, I am still dealing with this problem after 3,000 miles of cleaning the sensor. I am somewhat confident that the MAF is the problem for the exact reason forlooks said above. The chances that both O2 sensors went out is unlikely (from what I have read and makes sense). I have a OBD2 reader coming and I have read on how to read if the MAF is bad using volumetric efficiency. See below. It is from a e46 forum.

http://forum.e46fanatics.com/showthread.php?t=617788

I also decided to replace my "lifetime" fuel filter. I replaced that and then I cleared the codes tonight. It is still a work in progress, but if I don't figure out what is going on soon I will probably take it to my indy.

AchtungE60

My Bank1 Bank 2 was due to my intake manifold... DISA valve. Doubt it's your O2 sensors.
Forget that code reader get some BMW tools. Look.............You're not going to get this with any other tools that I've seen.

AchtungE60

See my post above. I assume you have an M54 design. The 525 and the 530 have the same exact engines nothing different besides DME software and phycial intake manifold components.

moyern83

Where did you get the software/tools from? Did it set you back much? I have looked into that and I debated about getting something specific to BMW. I found things on the forum that gave some help with just an OBD scanner. I figured if it was too bad, I could take it to a local mechanic.

Has it been worth the money for you?

AchtungE60

absolutely.....about 100 fold so far.

moyern83

Achtung,
Did you DIY for the intake manifold? I have had P0171 and P0174 errors as well. I have cleaned the MAF, changed the spark plugs, and now I have a new fuel filter in the car. The spark plugs and fuel filter were not really to take care of the codes, but a lot of people on here said the MAF needed cleaned with those codes. I have found on the forums that those codes would either be a MAF sensor bad or a vacuum leak (possibly via intake manifold). What are your thoughts?

AchtungE60

Yes I did the intake manifold when i did the valve cover gasket and plugs...I also took off the vanos unit and upgraded the vanos seals with besian's seals. cleaned out the entire vanos, put new seals did the intake manifold and cleaned it up. The intake manifold is a metal gasket and I didnt do that because it's not needed.

After you shut off the engine you should hear air sucking back....this is the DISA releasing pressure and that is working as designed. I have two of these cars 330 and 530. No problems at all.... Take a day, do your plugs and your valve cover gasket and also take out the airbox and drop a new filter and check hoses for cracks. Take off the DISA and make sure it's not broken and the flap is still spring loaded etc. It will be REALLY dirty. Anyway bosch platinum +4 plugs (OEM) are available for $5 each and the gasket is about $30 I mean the whole thing costs you about what $75 and takes 2 hours? It's worth it bro. Of course without BMW software tools you cannot reset adaption values but your car will still pur like a little kitty and drive like a panther....Didn't you do your fuel filter/sending unit or was that someone else? I'm doing this coming weekend.

BTW I had those same errors. Same exact errors kept coming and going prior to me doing the above. I just did vanos seals because they were laying around....not needed and if you've never take an engine apart not recommended lol.

forlooks

I've changed the sparks, coils, fuel pump & filter, water pump (metal propeller), radiator, & radiator hoses all at the same time (@ 90,000 miles). About 500 miles later i decided changed the Vacuum hoses on my own, which is common on the M54. While changing the vacuum hoses, i cleaned my idle valve & throttle and changed the throttle gasket. Then i got the lean mixture code on the O2, after all those parts and I've cleaned my MAF twice, prior to any O2 CEL. At that point i changed the MAF (got tired of cleaning, because cleaning was more of a band-aid rather than a real fix. The O2 code went away and hasn't shown up for the past 1,000 miles. Idle is more stable, better start up and smoother acceleration. I still have an idle issue at street lights, which will be my DISA (also another common problem). I will change that next too. I rather spend money on parts/preventative rather than paying for tow.

In short, from my experience, I doubt that the vacuum is causing your O2 CEL.