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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 07-17-2006, 06:05 PM
KTrostel KTrostel is offline
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P0173 - Fuel Trim Malfunction - Huh?

Just got a P0173 error code. The code reader says this is a Fuel Trim Malfunction - Bank 2. Doesn't really list a cause just that the whole fuel trim system on bank two went out. Anyone run into this before and if so, what was the cause?
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  #2  
Old 07-17-2006, 06:06 PM
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z0lt3c z0lt3c is offline
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fuel trim

Reset and see if the code comes back.

If it returns, my guess is the MAF.
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  #3  
Old 07-17-2006, 06:17 PM
The Other Tom The Other Tom is offline
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Quote:
Originally Posted by z0lt3c
Reset and see if the code comes back.

If it returns, my guess is the MAF.
MAF is most likely the cause. Another guess is dirty/clogged fuel injector. Almost has to be one or the other. For more info on what fuel trim is and how it works, connect to
www.ackthud.net/shawnfogg
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  #4  
Old 07-17-2006, 06:34 PM
Sc'd540i6 Sc'd540i6 is offline
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The Fuel trim codes indicate that the car is running excessivly rich or lean as indicated by the pre-cat 02 sensors. They only indicate a fault not the type. There can be many causes of this error, depending on which condition you are getting (rich or lean) everything from Manifold air leaks to faulty injectors and everything in between. A bad MAF may trigger the fault but its an expensive part to just swap out blindly.
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  #5  
Old 07-18-2006, 07:11 AM
KTrostel KTrostel is offline
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Initially I thought it was the MAF but I would expect both banks to have the error code. Vacuum leak sounds plasuable, dirty injectors - wow they would have to be dirty.

Has anyone used an in car fuel injector cleaner? Note - I do not mean an in the gas cleaner I mean a professional, disconnect the fuel line, self contained cleaner system.
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Old 07-18-2006, 08:53 AM
Sc'd540i6 Sc'd540i6 is offline
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Quote:
Originally Posted by KTrostel
Initially I thought it was the MAF but I would expect both banks to have the error code. Vacuum leak sounds plasuable, dirty injectors - wow they would have to be dirty.

Has anyone used an in car fuel injector cleaner? Note - I do not mean an in the gas cleaner I mean a professional, disconnect the fuel line, self contained cleaner system.
I chased these codes for months during my S/C development. While it would seem logical that leaks prior to the manifold (or MAF) would throw codes for both sides, don't use that as a rule. I found that my '98 would throw bank 2 codes several days eariler then bank 1, this could be attributed to differences in the 02 sensors, or just plain 'ol Bavarian black magic.

Good luck.
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1998 540i6
VF Supercharger 6psi
CDV delete (thanks Dave)
Rouge Octane SSK w/selector rod
Cluch Stop
3 spoke sport steering wheel
Euro Angel eyes
Smoked side markers
Buisness CD retrofit
IceLinkPlus (trunk mounted)
Staggered 18" HRE 547R's
Matte Chrome interior Trim
Billet Aluminum Gague Rings
Mtech Front end
35% luminar Tint
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  #7  
Old 07-18-2006, 05:47 PM
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z0lt3c z0lt3c is offline
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Quote:
Originally Posted by KTrostel
Initially I thought it was the MAF but I would expect both banks to have the error code. Vacuum leak sounds plasuable, dirty injectors - wow they would have to be dirty.

Has anyone used an in car fuel injector cleaner? Note - I do not mean an in the gas cleaner I mean a professional, disconnect the fuel line, self contained cleaner system.
I've had 3 BMWs which all did the same thing when the MAF went, threw out fuel trim codes that made no sense. I've talked to 2 different mechanics about this, and they both pretty much said if the codes didn't make any sense to suspect the MAF first.

In the case of my 01 X5, the car went into some kind of driving fail safe mode, and as soon as the MAF came out, it went back to normal driving (or so the bmw dealer told me -- al I know is I had a sleepless few nights consider a tranny swap on an X5). My e39's didn't do this however.

If you have a buddy with the same engine BMW you can swap MAFs. If you are in driving distance of western NJ you can use mine if you'd like. The job takes like, maybe 10 minutes.

You can sometimes find MAF's on ebay for $75-$150 although unsure they are new and/or guarenteed.
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  #8  
Old 07-18-2006, 08:59 PM
NeoCole NeoCole is offline
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Bank sides

Bank 1 is passenger side, Bank 2 is driver's side. Found this out with a CPS error.
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  #9  
Old 07-01-2016, 06:24 PM
grysbmw grysbmw is offline
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Quote:
Originally Posted by NeoCole View Post
Bank 1 is passenger side, Bank 2 is driver's side. Found this out with a CPS error.
Maybe on your vehicle, but not necessarily on all vehicles.

The trick is figuring out the condition based on the code...is the car running Lean or Rich. This will help a whole lot however I do not if there is a way to figure this out. If there is a way I sure wish someone would share the secret. I know it has to do with STFT, LTFT, and O2 sensor. What specifics would help us determine Lean or Rich condition? Anyone???
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  #10  
Old 07-01-2016, 07:53 PM
edjack edjack is offline
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Positive short term fuel trim = vacuum leak (the DME has to inject more fuel to counteract).

Negative = too rich; there may be a leaky injector, or other cause.
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  #11  
Old 07-01-2016, 08:19 PM
bobdmac bobdmac is offline
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Quote:
Originally Posted by grysbmw View Post
Maybe on your vehicle, but not necessarily on all vehicles.

The trick is figuring out the condition based on the code...is the car running Lean or Rich. This will help a whole lot however I do not if there is a way to figure this out. If there is a way I sure wish someone would share the secret. I know it has to do with STFT, LTFT, and O2 sensor. What specifics would help us determine Lean or Rich condition? Anyone???
Just out of curiosity, what prompted you to bring this up 10 years after the last post?
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  #12  
Old 07-05-2016, 09:52 PM
grysbmw grysbmw is offline
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Did not realize the post was that old...LOL! I have a bad habit of reading and responding. I guess I have been on Facebook just a bit too long. I thought it was a recent post. Y'all can ignore!
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  #13  
Old 07-05-2016, 09:56 PM
grysbmw grysbmw is offline
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Quote:
Originally Posted by edjack View Post
Positive short term fuel trim = vacuum leak (the DME has to inject more fuel to counteract).

Negative = too rich; there may be a leaky injector, or other cause.

Edjack, this is great info...so what does it mean with the short term fuel trim is positive at idle and negative at 2500 rpm? And we are talking full spectrum from a positive 27.3 to a negative 28.1? This is on Bank 1, Bank 2 is just the opposite negative 28.1 at idle and swings to a positive 27.3 at 2500 rpm.

Any thoughts?
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