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E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

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  #1  
Old 08-08-2010, 01:08 PM
scottshaw scottshaw is offline
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Location: Brentwood Tennessee
 
Join Date: Jul 2008
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Mein Auto: 2002 525i, 2001 330CI
P0102

I posted earlier today, but was a reply to a thread, so here is a new thread on this.
My 01 E-46 with new head gasket runs great, but turned on the MIL (service engine soon light) and has code P0102, Low voltage at Mass or volume Air flow sensor. I checked all the hose clamps they are tight. I put my hand over the air intake at idle and killed the engine and there was a strong vacuum on my hand for over a minute afterwards so I am sure there is no air leaks. I gently blew off the hot-wire in the MAS, but it already looked clean. This car has a Dinan air cleaner system in it. I don't think it was ever serviced as it was filthy and the paper filter is down in front of the front fender liner, so hard to get to. I cleaned the filter a few weeks ago, but did not re-oil it. Also, I noticed that I put the MAS on up side down previously, (wire connector on the bottom) the air flow was the right way, but since these use hot-wire anemometry to read air flow I thought MAYBE orientation was critical. I have re-mounted it properly, and I am about to oil the filter. One other thing, at about 1500 RPM under load I can hear a whistle, but I am not sure if it is just air coming around the partially open throttle valve or not. And if it IS leaking how can it hold a vacuum when I choke it by hand?

Any insights from the group would be welcome, orientation, oil on the air element? The E46 Fanatics site has a few postings about Aftermarket filters causing this, but I think this was an OEM modification as the studs where the original air box mounts don't even have the paint worn off of them.

The car runs great, but I need it to pass emissions which it won't do with the MIL light on!

Scott
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  #2  
Old 08-08-2010, 04:54 PM
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smolck smolck is offline
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Location: Birmingham, AL
 
Join Date: Jul 2007
Posts: 22,348
Mein Auto: 2004 ZHP Sedan
Quote:
Originally Posted by scottshaw View Post
I posted earlier today, but was a reply to a thread, so here is a new thread on this.
My 01 E-46 with new head gasket runs great, but turned on the MIL (service engine soon light) and has code P0102, Low voltage at Mass or volume Air flow sensor. I checked all the hose clamps they are tight. I put my hand over the air intake at idle and killed the engine and there was a strong vacuum on my hand for over a minute afterwards so I am sure there is no air leaks. I gently blew off the hot-wire in the MAS, but it already looked clean. This car has a Dinan air cleaner system in it. I don't think it was ever serviced as it was filthy and the paper filter is down in front of the front fender liner, so hard to get to. I cleaned the filter a few weeks ago, but did not re-oil it. Also, I noticed that I put the MAS on up side down previously, (wire connector on the bottom) the air flow was the right way, but since these use hot-wire anemometry to read air flow I thought MAYBE orientation was critical. I have re-mounted it properly, and I am about to oil the filter. One other thing, at about 1500 RPM under load I can hear a whistle, but I am not sure if it is just air coming around the partially open throttle valve or not. And if it IS leaking how can it hold a vacuum when I choke it by hand?

Any insights from the group would be welcome, orientation, oil on the air element? The E46 Fanatics site has a few postings about Aftermarket filters causing this, but I think this was an OEM modification as the studs where the original air box mounts don't even have the paint worn off of them.

The car runs great, but I need it to pass emissions which it won't do with the MIL light on!

Scott
The whistle is a classic sign of an aftermarket CAI. Dinan or not, it is just gonna do that, tradeoff I guess for the great sound at WOT. The MAF could be dead for a number of reasons, age, dirt, or just whatever.
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  #3  
Old 08-09-2010, 09:12 AM
scottshaw scottshaw is offline
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Location: Brentwood Tennessee
 
Join Date: Jul 2008
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Mein Auto: 2002 525i, 2001 330CI
Thanks smolck! Good to know that the Dinan sounds that way, I figured it must as I certainly could not find any leaks. My son goes to Bama by the way! Roll Tide!

Do you know if there is a spec for the resistance of the two hot wire elements? I have the Bently manual for this car but it does not say anything. I cleared the codes last night and it again lit the MIL this morning. The snap-shot of the even in the OBD-2 reader said that the RPM was at 1200 so it triggered it right at start up. I am surprised that the car performs well if the MAS is really bad, I drove it two weeks ago about 150 miles and it had really good performance and good fuel consumption, but I guess the O2 sensors really regulate steady state cruising more. I am a small engine fuel systems engineer, so i don't work with EFI systems but I have a pretty good handle on how they work. I also have worked with hot wire anemometers before so I know the concepts of how that MAS works. I am scared to just replace it as I have seen so many posts about it not changing anything, I would like to run some more diagnositcs before I jsut swap parts.
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  #4  
Old 09-24-2010, 07:25 PM
scottshaw scottshaw is offline
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Location: Brentwood Tennessee
 
Join Date: Jul 2008
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Mein Auto: 2002 525i, 2001 330CI
It WAS the MAS, I replaced it with an identical Siemens part for half the price of the BMW. Check engine light went off, I passed emissions the next day.
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  #5  
Old 04-05-2013, 10:19 PM
Luis0001 Luis0001 is offline
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Location: Los Angeles
 
Join Date: Apr 2013
Posts: 1
Mein Auto: 2001 bmw 325i
p0451

i got code p0451 how can i fix
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  #6  
Old 04-06-2013, 11:05 AM
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SJBimmer SJBimmer is offline
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Originally Posted by Luis0001 View Post
i got code p0451 how can i fix
Start a new thread so people can find it. You will also get maximum responses this way.
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  #7  
Old 03-07-2014, 11:57 PM
HuskyRossy1987 HuskyRossy1987 is offline
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Location: newport
 
Join Date: Jun 2012
Posts: 28
Mein Auto: bmw 318ci e46
I've got this problem with p0102
But my car seems to be overheating at first, changed the thermostat and bled the coolant, was ok for 2 days and then cut out when driving, connected my obd scanner an it was 111degrees
When it's cooled down, I keep losing power and jerking n stalling , it's doing my head in ATM, need desperate help
Water pump is working and have no major signs of head gasket either
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