BMW 2 Series AT Failure: When to Change Transmission Fluid

I had a similar issue with my 2018 BMW 3 Series diesel last year. The symptoms matched yours exactly, erratic shifting, warning lights, and limp mode. The diagnostic showed an undervoltage problem in the transmission control unit. Initially thought it was just the transmission fluid, but turned out the wiring harness to the transmission was damaged, causing voltage drops. The mechanic found worn-out connections and corroded wires. Had to replace the wiring harness and the transmission control module. While they were at it, they did a transmission fluid change since the system was already open. It was a serious job that took a couple of days to fix completely, but the transmission has been shifting perfectly since then. The worn wiring could have eventually led to complete transmission failure if left unchecked. Based on your symptoms, I'd recommend getting it checked by a BMW specialist who can properly diagnose the electrical system along with the transmission mechanics.

Thanks for sharing your experience! That's really helpful as I'm dealing with very similar symptoms. Glad to hear you got it sorted out in the end. Did you remember roughly how much the whole repair set you back? Also, has everything been running smoothly since the fix, or have you noticed any other issues pop up? I've been worried about potential knock-on problems and would love to know what to look out for.

Hey! Happy to give you an update. The total bill came to 240 € to fix that undervoltage problem. The mechanic sorted out the transmission oil issue too, it was definitely worn out like they suspected. Since getting it fixed, my 3 Series has been running like a dream! The shifting is butter smooth now, no warning lights, and zero transmission problems. It's been such a relief, to be honest. You know that feeling when everything just works the way it should? Haven't noticed any other issues pop up, no knock-on effects at all. The transmission's been working perfectly for months now. I was worried like you about potential problems down the line, but honestly, once they got to the root cause (that undervoltage issue), everything else fell into place. Quick tip though, I've been more careful about getting regular transmission fluid checks since then. Better safe than sorry, right? If you're getting yours looked at, might be worth asking them to check the wiring harness too. Could save you some headaches later on!

Thanks for the detailed info! Just got back from the mechanic today actually. Turns out my issue was different than yours, had a failed solenoid in the transmission plus some dirty fluid. The repair was pricier than yours, around 900 bucks total including parts and labor. They replaced the solenoid and did a complete fluid flush. Been driving it for a few hours now and what a difference! No more jerky shifts or warning lights. The mechanic recommended I get the transmission serviced every 50,000 km from now on to prevent future issues. Good call on that wiring harness tip, had them check it while they were at it. Everything looked fine there, thankfully. Really appreciate you sharing your experience, helped me know what questions to ask at the shop. Fingers crossed this fix holds up as well as yours did!