MAF, transmission light
 

2001 BMW X5 E53 3.0 160K miles
Got codes for MAF replacement.
Also, transmission light came on after changing bad alternator.
Disconnected battery & transmission light went off.
Past few days, car runns fine but transmission light came back and downshifts hard..
Replaced MAF & disconnected battery again and transmission light went off (shifts fine now) but truck runs like crap.
Bad acceleration, feels like misfiring

Scratching my head!

You need to scan for BMW specific codes. If you get a bad misfire the computer will shut down that cylinder and you'll get terrible performance. that will set off a ses light though so I'm thinking check fuel supply.

What brand MAF did you buy? I have seen a lot of cheap units cause huge issues. An OE manufacturer Siemens/VDO on sale at FCP Euro for $143 right now and has high marks as a replacement.

If it helps in the troubleshooting, your engine should idle just fine with the MAF disconnected. I've got a 2001 3.0i as well, and have done this many times. You'll get a warning message (I forget what), but it resets itself when the MAF is reconnected.

So if you can't idle well with the MAF disconnected, you've got other problems, and it may be easier to find and fix those problems before bringing the MAF back into the system.

I was going to mention: unplug maf to eliminate that variable


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I had AZ clear the codes in the system.
With MAF unplugged, truck still runs like crap, rough.
Transmission light came back on.
I know if I clear the light (disconnect neg terminal) the light will go off but still runs rough, even with MAF unplugged.
But as soon as I plug it back in, tranny light will reappear.|
Been through this a few times, same result.

I have to get the new codes read now.

got the codes read.....

now it shows cylinders 2,4 & 6 are misfiring w/fuel cut-off
random misfire detected
System too rich Banks 1,2




WTF, that wouldn't go bad all of a sudden.
ran good before MAF was replaced

very strange

- UPDATE -
Replaced MAF
Replaced plugs & coil packs
Had a leak so replaced radiator while i was at it

NOW - Started it up and it seemed to idle & rev great in park.
As soon as it went into reverse, it started to stutter.
The SES & transmission light came on AGAIN
I drove it around the block and it ran like crap.
I disconnected the battery to clear the transmission light and started it up again.
It still ran crappy
I disconnected the MAF and it bogged down a little & the transmission light came on immediately after.
If it was a bad MAF, what would it do?
Why would the Transmission light come on after disconnecting the MAF?
Wouldn't that mean the MAF is good?

A genuine Siemens MAF or some cheap ass crap bought on eBay or Amazon? If it's not a genuine Siemens MAF there's your problem.

I've got a 2001 3.0i just like you.

Just now, as a test for you, I went out there (had driven the car earlier, so it was warmed up), unplugged the MAF and drove it.

After starting it up, no problems at all. As soon as I shifted into R (from P), the TRANS. FAILSAFE PROG warning came on. I went on a little drive. The shifting was definitely affected, much clunkier shifts, which makes sense, since the TFP warning is that the system thinks something is wrong and is using the AT in a safe mode to prevent damage. But other than the clunky shifting, the car drove fine. As in the engine seemed perfect as it always is, smooth, powerful, no missing, no initial problems, no high RPM problems. Just fine. Now, I expect there is a loss in efficiency and probably high end power, but nothing I could tell.

And if your MAF is unplugged, it does not matter how bad it is (unless it is obstructing airflow, in which case you could just remove the whole thing). It could be completely dead and broken and if it's not plugged in, it won't be making anything worse, and the rest of the system can run just fine without it, as my test above shows.

So as I mentioned a few posts up, if you unplug the MAF and the engine won't idle and (as I now have confirmed) drive just fine, you've got problems beyond the MAF. You may have problems with the MAF too, but it only makes things tougher to solve multiple things at the same time. So I'd focus on fixing whatever is broken outside the MAF first.