[1stupidsailor]

I'm hoping this has been seen before, search didn't turn up anything for me...

I purchased a 100k '08 335i for a bit of a project car as well as something to reduce mileage I'm putting on my F30. A local vendor installed DPs, FP, and inlets for me, and I have an MHD tune, but have yet to beat on it with any of the parts or tune. Car drove fine for 2-3 weeks then pretty much out of nowhere, I get a 4-5 slip that goes from noticeable to jarring to dropping a trans fault within a short period, few miles. Only happened when the car was heated up, and not during WOT, I generally drive pretty mellow (I obviously didn't go WOT at any point after the first time I felt an issue). Codes were the 4F85 and 4F8A, so I took it in to have a look and did some research. Seeing that the VB contained the most common culprit parts, I ordered an entire VB from RevMax and shop installed it.

They put about 15 miles on it, no issues, looks like everything's fixed. I drove it home via a car wash and gas station, a 50+ mile mix of highway and surface streets with lots of stop and go, no issues. Drove it to work about 20 miles, again mix of highway and surface, no issues. On my lunch I went to ship back the core and made a couple other quick stops, and after a few miles I started to feel a bit more kick than normal. Couple more miles and some testing via the paddle shifters, it's back, 4-5 shift, just as before. Only a short distance back to work but the problem got worse, enough to finally toss the codes before I got to the parking lot. Again, I have not gone WOT yet, or even heavy throttle, and light throttle the vast majority of the time.

I've seen the VB as the most common fix, and it certainly did something in this case, but what else could have caused the problem to reappear? After 75 miles of mixed driving and not a single hiccup, then poof, here we are again during a quick trip on my lunch break. The shop reset adaptations and changed out about 2 quarts of fluid along with the pan/filter. I was able to drive it home today with no problems, mostly highway followed by about 5 miles of surface streets. Parked it and left it running, went and got tablet and hooked up MHD, trans temp was 187. Drove a short ways and it went up slightly to around 190, then the problem hit again. I was able to replicate it, same as before with the 4-5 shift. Temp when I got home was 207, total trip was maybe 1.5 miles. The only code that came up this time was 2AD0, unable to comm with TCU, nothing in the history for any of the failures today. From what I've found, those temps are ok.


Anyone had this experience before, problem disappeared then reappeared with a brand new VB? Thank you in advance!

Edit: MHD shows no history of any other tranny codes either, but the malfunction light has come on twice. MHD also didn't see the previous instance, though it did register the 2AD0 during my short drive.

Edit edit: Trans is 6HP21, prod date was 5/08.

[1stupidsailor]

Edit again. Took it out, starting cold, to go and try to recreate it and log trans temps. Started getting the hard shift as low as 150, noticed that it seemed to be load dependent. I would get hard shifts that didn't trigger the malfunction, then on the next acceleration it was normal. All shifts seem to be a little rougher though, especially when using the paddles, (not sure how the E90 normally behaves), so I'm kinda leaning towards fluid, hard to tell if there's any whining over the intake.