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raider03 03-29-2013 01:03 PM

2001 BMW X5 3.0i running lean!
Hello everyone new to the forum... Few weeks ago bought a 2001 BMW X5 3.0i w/ 108K miles on it. Love the car, but it started throwing P0171 & P0174 codes and they are giving me quite a headache. First thing that came to mind was dirty/bad MAF so I cleaned it out and reset the codes. Went with 2 days without SEL and came back on. I didn't really had any symptoms before or didn't notice any... Now I do feel a small rough idle.

I've visually checked for cracks and also sprayed brake cleaner and can't find any leaks on major intake hoses. I also took out the dreaded DISA valve and looks just fine to me. I have a scanner and was looking at my O2 voltages and all 4 sensors are at .03-.04 is this normal below the 0.1volts?? I knw it means system is lean but all O2 sensors including downstream? Thinking it might be the Front O2's .

Another weird thing I noticed, I unplugged the MAF while car is running and engine didn't turn off and I looked at my front O2 voltages and they went up to .4 - .8 instantaneously , if I plug the MAF back in engine shuts off. So I thought it was a bad MAF and went to dealer where I bought the car and they switched it with another X5 they had in the lot and I took readings and the issue is still there.

Would appreciate some guidance. Thanks.

buster1015 03-30-2013 06:54 PM

I went through similar issues on my X5 last year. I was getting lean fuel trim on both banks. I first replaced the O2 sensors on both sides. The change interval is about 100k miles. If you don't have a record of replacing them I would suggest you go ahead and replace the upstream O2 sensors which are before the cats. It is unnecessary to replace the after cat O2 sensors because they are only used to determine if the cats are working and will not cause your issue. Also, since they are exposed to much lower temps they tend to last much longer.

Since you swapped in a known working MAF that is unlikely to be you're issue.

If the O2 replacement doesn't solve the problem the next possibility is a vacuum leak after the MAF so that un-metered air is getting into the system and the computer is not able to add fuel to account for it. One method to check this is to lightly pressurize the intake system to a few psi or so and spray some soapy water at connections. I found that the connection just after the MAF was leaking on my car and replacing the internal rubber seal fixed it. There are other methods using a smoke generator but hopefully you won't have to go to that effort.

408sanjosebmw 03-30-2013 07:07 PM

Buster1015 hi im new here to my bmw x5 its giving me the same code p1747. Did you find out to fix it? Thannks

buster1015 03-30-2013 10:44 PM

My problem was solved by replacing my MAF and replacing the sealing ring just after that.

The p1747 code you listed is associated with the transmission, sometimes activating the Trans Fail Safe Mode. If that is your problem you should start a new thread and explain your symptoms.

But, if that was a typo and you meant p0174, it means 'System Too Lean (Bank 2)'. Bank 2 is the driver's side. How many miles do you have on the car?

raider03 04-01-2013 12:27 PM

Buster1015, couple of questions.

I really want to replace O2 sensors but at the same time be sure that I have found the culprit as parts are expensive. Just one thing though on Sat the code switch to lean on bank 2 (p0174) and STFT was perfect on bank 1 and bank 2 was +20 what gives? and then Sun. and today back to lean on both banks.

2nd question, by any chance, have you ever unplugged your MAF and looked at O2 voltages on scanner? do they stay the same or there is a difference? I am asking this because when I unplug MAF my O2's are around .7 - .9 running rich on both banks. But if I plug in MAF O2 voltages drop to .03 - .05 not even the normal lean which is .1 volts.

X5 E53 Driver 04-01-2013 01:37 PM

I had same this problem and I found that I have air leak in the air intake boot since I replace it its alright now.

raider03 04-01-2013 02:11 PM


Originally Posted by X5 E53 Driver (Post 7487184)
I had same this problem and I found that I have air leak in the air intake boot since I replace it its alright now.

Ugh I wish my problem would of been as simple as that... Unfortunately I checked all my vacuum hoses and all seem fine.

Hopefully someone in here could do a quick check for me and have there MAF disconnected and check voltages for O2 and then reconnect MAF and recheck voltages of the O2 to see if there is any voltage differences.

buster1015 04-01-2013 03:42 PM

I feel the same way with trying to avoid replacing good parts. Although, I only spent about $45 each for the Bosche O2 sensors. They are much less than the OE ones ($130?)and are identical except won't have a BMW logo. BMW uses Bosche O2 sensors as OE. Because both the O2 sensor and the MAF degrade slowly over time either can be causing your problem. More importantly, even if you detemine which is the culprit the other may cause you grief months later. Do you have any repair records? I would check with that dealer and see if they have any records for the replacement of those parts.

When the MAF is unplugged the computer will revert back to a 'standard' fuel map. I'm not sure but would guess that when everything is functioning there should be little change at idle so O2 sensor values should not change a whole lot. I'm curious so I'll try this tonight and let you know what I get. I have a non BMW scanner that works with a laptop which gives me the O2 fuel trims, not sure if it will give me the voltages but that will still help figure out what should happen with/without the MAF.

raider03 04-01-2013 04:53 PM

@buster1015 Thanks for helping out & understanding I really appreciate it. Really want to get to the bottom of this as I am going thru gas tanks super fast due to the high fuel trims.

Also where did you buy your O2's? My local autozone has the OE bosch for $70each. Thanks!

buster1015 04-01-2013 07:10 PM

1 Attachment(s)
I had bought them from

When my engine is idling the STFTs are about zero varying to +2 and -2. I pulled the MAF connector and the engine revved up to 1100 rpm briefly and quickly resettled at the normal 600 rpm idle. The 15 seconds after pulling the connection the STFTs varied from +3 to +7. Engine idle seemed smooth but the computer continued to adjust the fuel and by the 30 second mark STFTs were -3 to -6. I didn't try to plug the MAF back in while the engine was running but I think there is a good chance that would stall the engine.

I hadn't thought much about your mentioned O2 sensor voltages because I've been working with a wideband O2 while tuning my Porsche lately. The narrow band O2 (type used for fuel trims) is really only good at telling the computer if the engine is running rich, lean, or at stoichiometric. I uploaded a generic O2 output voltage chart. As you can see stoich includes a large range from about +.15 to +.75v. I'm sure the Bosch one is very similar. Your O2 voltages could be due to the sensors going bad OR the sensors are completely fine and you have a different issue (MAF, vacuum leak, clogged fuel filter). At this point we can't tell for sure which cause is giving the lean reading since your voltages are within the typical range.

Attachment 369353

There is a way to test the MAF and get an idea if it is working. The basic idea is that the MAF signal varies from 0 to +5v based on the mass air flow rate. Voltage at idle should be low (~1.5v) and close to max (>4v) at wide open throttle. Instead of describing it I found a video that shows the test procedure:

You mentioned high fuel consumption. If the O2 sensors were incorrectly reading lean when there is no real issue then that will prompt the computer to add more fuel (too much) and your fuel consumption will increase but I would guess throttle response and power would still feel okay.

If the MAF sensor is under estimating the airflow (or air leak) then your O2 sensors would be adding fuel to get close to stoich. This was my issue and my fuel consumption went down and I began to notice decreased power at WOT.

raider03 04-02-2013 04:12 PM

Thanks Buster1015 for the help...

Today once again bank 2 is lean. Before I order new O2 sensors, I will try to smoke the intake system to make sure I didn't miss any leak. Going to have to create my own machine though, Indy shop wants to charge $90 to smoke.

Another thing from today when I started up this morning checked codes and there was pending codes for misfires on Cyl 4, 5, & 6(bank 2). P1348, P1350, P1352. Guessing this is from the false lean condition the computer is creating or there really is a big vacuum leak according to the O2 sensors (since they are reading below .1 volts. and stay in that range @idle).

Scott ZHP 04-03-2013 07:15 AM

Double check yout LOWER intake boot, especially the little accordian elbow that's attached to it. If it is original, it likely has a crack in it.
These boots are notorious for throwing lean codes. It's located waaaaay down in the engine bay and is attached to the throttle body; I'm not talking about the plastic one connected to the MAF, it's below that.

upallnight 04-03-2013 09:34 AM

If only one bank that is lean I would look at the disa valve to see if the flap is operating or stuck. While you are at it, when you remove the disa valve there should be some resistance, there should also be some resistance when you re install the valve. If there isn't any resistance, the problem is the seal between the valve and intake manifold. You can replace the disa valve or you can replace the seal with an o-ring. Just Google or Youtube disa valve o-ring.

raider03 04-03-2013 10:16 AM

Yeah that was one of the first things on my check list. The O-ring was pretty worn so I made a new gasket with Ultra Copper but didn't make any diff.

One thing I noticed when I took the DISA out, it was dirty with some oil so I cleaned it out. Is there suppose to be some kind of dirty/sandy oil in the intake manifold?

upallnight 04-03-2013 01:10 PM

Probably didn't make a different because the seal between the disa and intake manifold is an o-ring, not a gasket. Since there is only two screws and the surfaces are not machined, you still have a vacuum leak there.

raider03 04-06-2013 10:28 AM

@upallnight thanks for the help. DISA is working properly.

Had a smoke test done, and seems my Valve cover has a crack in it -___- great. $300 part. LOL I'll have the dealer pay for that...

Scott ZHP 04-08-2013 07:16 AM

Just FYI... the actual DISA itself makes no difference and won't throw lean codes. It's only purpose in life is to alter the intake charge through the runners based on engine rpm. The factory DISA seal is molded into the housing and is pretty durable. If this seal is leaking air, it could throw a code. If your X5 has more than 100k miles on it, the DISA nylon bellcrank/plastic flap assembly is probably worn out and needs to be rebuilt. Gary at German Auto Solutions makes a rebuild kit worth every cent.

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