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Discussion Starter #1
Hello all,
First time poster and first time BMW owner. We have a 2002 325xi for my kids' daily driver. While leaving the neighborhood, the CEL came on along with the transmission cog light. Car stopped moving. After turning off the car and letting it sit for a while (as per the manual), the cog light cleared and the car was able to drive back home. I checked the CEL codes this morning and found the following codes along with the cog light back on:
P0491 - Mass air flow sensor low flow limit detected bank 1
P0492 - Mass air flow sensor low flow limit detected bank 2.

I cleared the codes and tried shifting the transmission through all the gears. When moved to "manual" S D is displayed before cycling through M 1-3. I decided to try and clean the MAF. I have read on the forums that the MAF and can and can not be cleaned with MAF cleaner depending on the thread I found. After cleaning the MAF and re-installing, the cog light disappeared, but transmission still showing S D when shifted to "manual". If the car is rev'd to ~ 1500 rpms, reverse will start to grab and then give way, same deal with third gear. I know based on what I have read that the MAF is used to calculate the engine load and then in turn regulates whether the transmission will work or go into safe mode.

So my question is, do is still have a MAF issue even though i have yet to throw and set of codes? I have pulled the battery cables to reset the computer, but the trans remains in safe mode. Scanner shows the MAF reading at idle is ~ 3.2. Not sure if this is good or bad. I saw a spike of ~ 5 while rev'ing the engine. Since I can not drive the car, I can't get any different readings.
 

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I think you have two separate problems. Trans and MAF or other.
You don’t say how many miles on the car, unless I missed it.
The auto trans is not the strongest component to start with and it is further weakened by BMWs lifetime / no fluid change mantra of the era. If that trans has never been serviced then the life of the lifetime fluid may have been reached and with it the life of the transmission.
First thing I would do is check fluid level. Next I’d try a fluid change (change not flush) cuz it sounds like there’s not much to lose.
The MAF, if it runs better with it unplugged, is likely toast. Don’t buy autozone grade, should only be OE or OEM. Not my area of expertise, someone will likely have other and better suggestions. That being said, if trans has gone **** up, that should be the main concern.


Sent from my iPad using Bimmerfest
 

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Discussion Starter #3
Thanks for the reply. I forgot to mention the mileage in my previous post. The car has ~ 180k miles on it. I am pretty sure the transmission fluid has not been attended to since it is rated for "life" per BMW. I have seen other posts saying to replace the fluid and at the very least check the level.

It has also been brought to my attention that my codes in question may pertain to the secondary injection. I am guessing that is the same thing as the secondary air pump. I can hear it turn on during the cold startup, but I do not know how efficient it is working. Can the air pump cause the transmission to go into safe mode?
 

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Unplugging the MAF forces the engine computer (DME) to use a rich fuel/air mixture. So, if the engine runs better with the MAF disconnected it does not mean the MAF is bad! It means that the engine needs an overly rich fuel/air mixture. In E46Fanatics you mentioned a low MAF reading. I noted that at idle the MAF should be indicating about 3.9 grams per second of air at idle.
 
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