No Transmission Display, No Start ?

[T444E]

My 745Li (long wheel base beamer) has been sitting in my driveway for a few months and it always started.
Today it didn't. I charged the battery and still nothing.
I see a bunch of errors on the iDrive regarding the servotronic, dynamic drive etc but the most concerning is the No Transmission Display and the PRND flashing on the dash. And hitting the button does nothing.
After a few minutes the dash PRND stopped flashing and the error on the iDrive went off but it still wouldn't start

Where do I start

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[jclausen]

The battery has to be top condition charging the battery just tells you nothing you need to load test the battery if the battery is over 4 years old it’s done also they upgraded the lead acid battery to an agm because of the electrical demands of the car. Plus the battery has to be registered to the car. Finally if you are going to park this car for long periods install a battery tender and on the inside of the trunk passenger side behind the trim panel is a large fuse box stick your head in ther and look up there is a battery switch also called an airport switch when you use this it reduces the amount of electrical devices that the battery has to power while parked

[T444E]

This car is driving me bananas.
Over the summer it started fine and I drove it a couple times and no errors other than the suspension because it has a broken sensor on the passenger side control arm.

Now it won't do anything.
Yesterday I could hear the starter click like it didn't have enough juice. So I let it charge over night and put a jump pack on it this morning and all I get are error codes for everything.
And the starter doesn't even try to engage when I hit the start button
Also my generic code reader doesn't connect all of a sudden.

I'm at a total loss

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[T444E]

I got the obd reader to communicate, it had a P1720 code which is a failure in the can bus.
Once obd worked, the trans PRND stopped blinking but it still wouldn't fire over

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[jclausen]

These are complicated cars I would tow it to a good independent garage for diagnostics

[T444E]

Had it scanned with INPA/Rheingold, there were a million other codes but this one stood out most.

Yesterday it started up



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[T444E]

Seems the dme isn't being woken up
Wondering if there's a bad relay

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[T444E]

New battery, same issue

If I just wait until the PRNDL stops flashing on the cluster, it starts every time and all the errors disappear from the iDrive

There's some sort of comm error that I can't figure out here.

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[jclausen]

The bus systems are very complicated it, if it sat out side and it rained I look in trunk for water damage, check the carpets to see if there wet and lift the rear seat and set if there was any water under it

[Sleepyhead97]

New battery, same issue

If I just wait until the PRNDL stops flashing on the cluster, it starts every time and all the errors disappear from the iDrive

There's some sort of comm error that I can't figure out here.

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Next step is replace relays right? Check for critters chewing the wiring. Check connections make sure no corrosion at connections. After that. Have dme tested. Just saying what i would do im not a bmw tech.

[Sleepyhead97]

Anyone have ideas? I call dibs on that 7 hundo of my idea works

[T444E]

Sitting in this pile of shi1t,
I keep hitting OFF for the HVAC and it keeps turning it on 11 blowing air in my face with the engine off

This is cursed

But at least the seat heat works while I write this

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[tiMASTER]

The way our weather has been going, I'd be digging into the thrilling task of going through "component locations" in the ETM, and then unplugging each thing, checking/cleaning/drying/adding dielectric grease/re-installing them.

It should only take a month or so. And you should find critter chew along the way, if any.

Sorry I can't be more help.