Now, this is an interesting problem because, as he informed me, the key still worked for locking and unlocking the car. So, the key fob clearly had a heartbeat, but keyless comfort access was having none of it. I instructed him to place the key on the designated spot on the steering column and try to start it manually. Nothing. I told him to try again at different angles. Still nothing. At this point, I was beginning to suspect the car simply had it out for him.
Having encountered this particular gremlin before, I asked if he had a second key to test. No joy. Still nothing. And, of course, the car was parked in an underground garage, where towing it out would be about as practical as towing the Titanic with a Vespa.
So, I did what any sensible BMW tech would do—I drove over and disconnected the battery. Why? Because BMW software sometimes behaves like a moody teenager: give it some alone time, and it might just sort itself out. So, we stood around, engaged in the ritualistic 20-minute BMW owner chat (mandatory, by the way), then reconnected the battery. Viola! The car started on the first push. The owner looked at me like I had just performed some kind of ancient Bavarian witchcraft.
But, as always, the story doesn’t end there.
The Plot Twist: Software Gremlins
I had seen this issue before, and it was always tied to a software bug in the Body Domain Controller (BDC) module. BMW issued a Service Bulletin about this way back in August 2020, which means they were aware of it and, in typical fashion, pretended it wasn’t their fault. Every case I’ve dealt with had software from 2019, 2020, or early 2021—so updating the software was the fix.
But here’s where things got weird. This M340d already had the updated software. In fact, I had personally flashed it with I-Level 24-07-530 just a few months ago. Theoretically, this problem should have been eliminated. Yet here we were, staring at an M340d that just ghosted its own key.
I had only one move left—update the software again. The next available version was 24-11-5xx, so I went ahead with it. Did this actually fix the issue? I have absolutely no idea. But the car has been working fine for a week, so let’s call it a win... for now.
Lessons in BMW Survival
I gave the owner some life-saving advice: get a key card and install the digital key on his iPhone. Why? Because when the car decides to pull this nonsense again (and it will), he won’t have to call me in a panic. I also gave him a quick tutorial on disconnecting the 12V battery—because, fun fact, these cars have both 12V and 48V systems. But in this case, pulling the 12V battery in the trunk is enough. Also, a helpful tip: even after disconnecting the battery, the car will still have power for about a minute. Because BMW.
Now, for the ISTA enthusiasts out there, yes, you can also perform a BDC reset via "Call up ECU functions." This does the same thing as disconnecting the battery, but without all the heavy lifting.
The Unexpected Bonus Gremlin
Here’s another kicker. When the car fails to detect the key inside, it might just lock itself with the key inside. Yes, really. At that moment, the key card and digital key still work to start the car, but if you don’t have those? Well, you’ll need a locksmith, a lot of patience, or a very large rock.
In this case, my customer had neither the digital key nor the key card, so let’s all take a moment to imagine his reaction if that had happened. M340d locked in a garage, key inside, no way to start it. A perfect storm of Bavarian mischief.
For now, the car is running fine. But if anything changes, I’ll update you all. Until then, keep your key cards handy, your digital keys installed, and your battery terminals ready for a tactical disconnect.
Because in the world of BMWs, you never know when the gremlins will strike next.
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