[RocketSurgeon]

I have a BMW e66, a 2003 745Li here giving me fits. It came in completely unable to shift into gear. If you hit the column shifter, it would display D or R for a split second, but shift to park immediately without being able to drive a single foot. I replaced the valve body, mechatronic/bridge/tube seals, fluid, and filter/pan. The car was then able to drive about 3 feet before slamming back to park. There are no codes in the transmission, but the gear indicator lights on the dash begin to flash. Believing that we had a line pressure issue, I swapped the complete transmission, but it is still doing the same thing. It will shift into D or R for a few seconds, you can feel it engage the gear and transfer power, but after a few seconds sitting or a few feet driven, it slams back to park. What could this be?

[PelsonBMW]

did you tried to fasten your seat belt ? and then try to drive ?

[Powerlab]

Did you replaced the shifter with new one?

[Node]

Have you read faults at all??? Or just launched parts cannon??? Then there is still more than half a car to be replaced

IMHO 99% of time such behaviour is intentional "safety" feature due to some fault like missing/invalid CAN message, etc.

Could also be a faulty shifter constantly sending park command what is ALSO (usually) seen in diagnosis as park button always pressed.

[bmchicago]

have you checked the alternator? Full fielding?

[RocketSurgeon]

did you tried to fasten your seat belt ?  and then try to drive ?

I did try with seat belt fastened, though I will repeat that and confirm via live data that the car confirms latching.

Did you replaced the shifter with new one?

I have not tried replacing shifter or SZL yet. I did watch live data on the SZL and it appears to be reporting correct positions/presses.

Have you read faults at all??? Or just launched parts cannon??? Then there is still more than half a car to be replaced

IMHO 99% of time such behaviour is intentional "safety" feature due to some fault like missing/invalid CAN message, etc.

Could also be a faulty shifter constantly sending park command what is ALSO (usually) seen in diagnosis as park button always pressed.

I read codes and combed through live data first. Honestly the lack of transmission codes really threw me off. The behavior was consistent with a bridge seal failure. I checked shifter live data, and as far as I can tell, it appears to be functioning correctly.

What you mention with a safety/CAN anomaly sounds about right. When looking at EGS live data, the "auto-P" signal sometimes flickers for an almost imperceptible instant. What signals from the car could direct the EGS to shift to P? It does have a restraint system code for lost communication with driver door satellite...

have you checked the alternator? Full fielding?

It puts out voltage, but I haven't checked any deeper yet.

[kuno24]

Driver's door closed status?

[Node]

Well, if you would read "Fault profiles, electronic transmission control (EGS)" document, the list of reasons for P engagement could be like (message - unit):
FAT_door_switch_status CAS
Transmission_Park_position_control EMF
Peak_reduction_priority_control Power
Transmission_selector_button_P_1_operation SZL

Moreover the signal for example from SZL to EGS goes like:
Signal path: From SZL (steering column switch cluster) -> data bus BYTEFLIGHT -> SIM (Safety Information Module) -> data bus BYTEFLIGHT -> ZGM (Central Gateway Module) -> data bus PT-CAN -> EGS (Electronic Gearbox Control).

So you have plenty of potential suspects. I would even include that missing driver door satellite in case it is not fully dead, but rather sends all kinds of crap messages to SIM causing SIM to randomly freak out and send other crap messages down the path (like auto-P due to collision or something)...

---

P.S. I would start disconnecting those modules (including that door satellite) one by one and checking whether transmission started to behave. Of course disconnecting CAS is probably not reasonable to be tried first  That can also be checked in CAS live data how it sees door statuses.
P.P.S. I would start from that door satellite... IF that is the only fault there is.

[2013m5]

Safety feature:
. Car door open => Transmission shifts to park.

I agreed with Node check door satellite.

[RocketSurgeon]

I checked door status in the CAS and found the passenger rear door was "status 3" rather than reporting open or closed. Replacing a fuse now has all doors accurately reporting closed status, but transmission problem persists. I have a seatbelt warning and a misfire that I'll chase next.