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

Originally Posted by scottshaw

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.

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.

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.

i got code p0451 how can i fix

Originally Posted by Luis0001

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.