[FailureIsMyPassion]

Hi all, I have a 2011 335is with a DCT and it currently has some issues with reverse and first gear. At times the car would go into first and doesn't like it so it stays in 2nd. This usually happens when slowing down, but I think its happened a couple times when idling. When I try reversing, the car will randomly go into neutral and the light on the gear shift would blink and the box around the gear in the cluster blinks. The car literally gives me zero warnings and checking ISTA I get no fault codes related to the trans. These problems seemed to be mostly random, but I was able to get the car to go into neutral consistently when trying to reverse into my garage since it had to go up like a 2in step.

I took the car to BMW and they found that the transmission was leaking and low on oil. They wanted 7k to pull the trans and replace gaskets, so I did it myself. I took the trans out, checked the clutch and it looked new (only 46k miles after all...). The gears also looked fine, and there was minimal metal on the 4 magnets. Since I thought everything looked good mechanically, I decided to just clean the magnets, replace the valve body, filters, the mechatronic sleeve and pan gasket.

I put the trans back in, filled it with oil (~7.5-8L) while following the oil balancing service function and everything seemed to work fine, the car was able to reverse into the garage no issue, but after some more testing, the transmission will still randomly go into neutral or not liking 1st. I also tried resetting the torque curve and re-adapting the clutches, but nothing changed.

If you had a similar issue please let me know or if you have any suggestions for what I should try next. If any extra info or pictures are needed please let me know.

Also, on a side note, does anyone know how to properly keep the car in neutral when turning off the engine? I held the mechanical release under the shifter and it seems like I broke the parking lockout :/

[ptpending]

such a glitches with bmw gearboxes can be seen when engine has issue with grounding to body and/or ignition coils also have their ground not to attached to engine properly as well. that lead that some high voltages are going not a designed way

[FailureIsMyPassion]

Originally Posted by ptpending

such a glitches with bmw gearboxes can be seen when engine has issue with grounding to body and/or ignition coils also have their ground not to attached to engine properly as well. that lead that some high voltages are going not a designed way

Thanks for the suggestion. I took a quick look today with a multimeter and the ignition coils have continuity with the ground stud and I checked continuity for the engine using the cylinder head and it seems to be fine. I'll test the voltage drop tomorrow along with taking a look at the ground straps, which if I remember correctly were blue so that might be something.

If you have any suggestions on any tests I should be trying or some common failure points I should be looking at, please let me know.

[ptpending]

Originally Posted by FailureIsMyPassion

Thanks for the suggestion. I took a quick look today with a multimeter and the ignition coils have continuity with the ground stud and I checked continuity for the engine using the cylinder head and it seems to be fine. I'll test the voltage drop tomorrow along with taking a look at the ground straps, which if I remember correctly were blue so that might be something.

If you have any suggestions on any tests I should be trying or some common failure points I should be looking at, please let me know.

you have to check this not using multimeter, but physically, if all ground connectors are attached to ground points and there is no any movement at all

[FailureIsMyPassion]

Originally Posted by ptpending

you have to check this not using multimeter, but physically, if all ground connectors are attached to ground points and there is no any movement at all

Makes sense, will check this out soon.

As for updates so far, I did look under the car and ground strap was slightly blue near the mount points and the bolts were somewhat rusty. Will upload photos at some point.

The dealer also had the car for the past couple days and they suggested it could be a LIN bus issue with the GWS, but they said they werent able to reproduce the issue when they had the car… But its another avenue I’m going to try since I was already planning on sniffing the CAN and LIN bus anyways.

Also, not 100% sure if they mean the LIN bus between the GWS and the parking lock or if there is another line that goes to the parking lock to the DCT, but I’m leaning towards maybe the latter since I replaced the parking lock already and there was no change.

EDIT: I tested the ground points for the ignition coils and they had no play.