locomotiveBart

So the trans in my 545 decided it wanted a divorce from the rest of my car at the end of June. The dealer had it for 3 weeks and replaced the trans with a used one (dealer warranty). Within 100 miles after getting it back the car went back to the dealer because it would surge in 5th gear. Getting the car back tonight and what they told me was that they opened a puma case with BMW and that BMW allowed them to completely erase and reprogram the mechatronics unit (which they claim they are never allowed to normally do). Does this make any sense? I will not get to drive the car until tomorrow to see whether it is indeed fixed or not, but most of the surging issues I have read about here have required the mech unit being replaced.

top6491

Curious as to what you mean by surging. My 545 likes to surge slightly back and forth between 35 and 60 MPH (in D and DS modes). It does so on a farily rythmic basis, about every 10 secs or so. Nothing unsafe or bad, but you can feel it and it drives me and any passengers crazy. Only does it when I am driving at a farily steady speed. It doesn't seem to do this while I am accelerating. Sound familiar? I would aldo then be interested in this Mechatronics issue? PLease keep us posted.

locomotiveBart

The surging is exactly what you are describing. From what I have read it is actually slipping while in 5th gear. In DS mode our cars do not shift to 6th so that is the best mode to diagnose it. Mine however would do it while accelerating in fifth but not as bad as when cruising. About every 5 to 10 seconds, I would feel the car nose dive a little and then pick right back up. I'll let you know how it drives with the reflash tomorrow. I've read quite a bit about a failed mech unit causing but this is the first time I've heard of erasing and reflashing it as a fix. (not jut a software update).

turboawd

is it more like the torque convertor is locking and unlocking. is it almost like the rpms rise slightly when it occurs?

locomotiveBart

That's what it feels like, but if I understand correctly, the torque convertor does not lock up in 5th. Rpm,s jump about 100 to 200.

turboawd

pretty sure the convertor locks up. and when the rpms go up, it unlocks. you can tell cause if you're in fifth and give a little gas, the rpms will only go up as you increase speed, but when the convertor unlocks, you can give it gas and see the rpms raise a bit without the car accelerating propoertionaly.

locomotiveBart

Not sure how it would shift to 6th if the convertor locked in 5th. I've been wrong before though I'll pay closer attention to what it does and if it's fixed tomorrow.

locomotiveBart

And I'm pretty certain my surging was not the convertor unlocking as every time it does it, the car seemed to actual decelerate for a second. You could actually feel it push you forward in the seat. Strange feeling actually, not like downshifting or going to neutral, but more like resistance being added to the drivetrain and then removed.

locomotiveBart

I stand corrected. The converter will lock up in every gear from 1st to 6th. Guess you learn sumpin new every day.

http://www.e90post.com/forums/attach...7&d=1139956533

turboawd

most newer transmissions are designed that way for better fuel economy.