[AndrewC1989]

2015 328dx 8AT - 85k miles
Kerma stage 2 added ~ 3 months ago
Trans service done at 70k

Tonight I was parking in reverse on a slight incline and the trans slipped into neutral by itself. I tried to put in back into R and I could not. I drove away in drive and got two codes thrown on my idrive. They are posted below from BimmerLink. I shut the car off and turned it back on and all is normal. Should I be concerned? Is this something others have experienced? And if so, what was the issue? Could this be something as simple as needing an adaptation procedure? Or is this my transmission on its way out?

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[kdog_x]

My car just recently had a similar issue. I pulled into a tollway oasis, went to put it in reverse to pull out of my spot and it grinded, thought I had run over the parking block or something (though my car is too low to get over most parking blocks lol). Got out and looked, clear of the parking block. Hopped back in and went Park->Neutral->Reverse a few times with the same noise, car wouldn't move. Shut off the car and restarted and it went into reverse fine.

I ended up rebuilding the transmission mechatronics unit with new solenoids and a zip kit to resolve the issue. The car was also shifting harshly on the 1->2 shift, the 2->3 shift, and downshifts in the low gears so I suspected issues prior to this occurring. My mileage was about 230k, with changes every 60k since new.

I would suggest checking the fluid level first and inspecting for any possible leaks... Fluid should drip out of the fill plug with transmission oil temp warmed to 40* C. That wasn't my issue, but low fluid will cause a variety of shifting issues. Did you use ZF8 fluid when you changed it?

The mechatronics seal is a place where these transmissions are rumored to leak and should also be inspected. The mechatronics seal is the grommet that the electrical connector on the back of the transmission plugs into, I would inspect that closely. If there's any evidence of leaking under that connector that's likely it. I never replaced the seal until I rebuilt the mech unit, but it can be replaced while you have the pan off to change the fluid.

[AndrewC1989]

Originally Posted by kdog_x

My car just recently had a similar issue. I pulled into a tollway oasis, went to put it in reverse to pull out of my spot and it grinded, thought I had run over the parking block or something (though my car is too low to get over most parking blocks lol). Got out and looked, clear of the parking block. Hopped back in and went Park->Neutral->Reverse a few times with the same noise, car wouldn't move. Shut off the car and restarted and it went into reverse fine.

I ended up rebuilding the transmission mechatronics unit with new solenoids and a zip kit to resolve the issue. The car was also shifting harshly on the 1->2 shift, the 2->3 shift, and downshifts in the low gears so I suspected issues prior to this occurring. My mileage was about 230k, with changes every 60k since new.

I would suggest checking the fluid level first and inspecting for any possible leaks... Fluid should drip out of the fill plug with transmission oil temp warmed to 40* C. That wasn't my issue, but low fluid will cause a variety of shifting issues. Did you use ZF8 fluid when you changed it?

The mechatronics seal is a place where these transmissions are rumored to leak and should also be inspected. The mechatronics seal is the grommet that the electrical connector on the back of the transmission plugs into, I would inspect that closely. If there's any evidence of leaking under that connector that's likely it. I never replaced the seal until I rebuilt the mech unit, but it can be replaced while you have the pan off to change the fluid.

When this happened to me there was no noise or grinding at all, the car just slipped out of gear rather gently. I also want to note that this has happened to me more than once, however in the past I have been able to just put the car back into R and there were no codes or lights thrown. Also I’ve noticed that each time it’s happened, it’s always been on an incline, never on a flat surface.

I don’t wrench on my car myself so I can’t tell you what fluid was used and if enough was added, a mechanic did that for me. I’m pretty sure they used a kit from FCP euro in which case the correct fluid should’ve been supplied. Hoping this is a quick and easy fix, I’m only at 85,000 miles so I’d be very surprised/disappointed if this ends up being an expensive/serious issue.

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For this scenario, if it were my car and the fluid level is correct, I'd want the car to be scanned with ISTA to determine the conditions under which the errors happened and have ISTA run the test plans designed around these codes. Implausible gear ratios can mean a lot of things, including sensor disconnected, or loss of fluid pressure, or other things.