BMW M4 Electrical Chaos: Purple Xenons & Signal Problems

Hey there! I had a similar issue with my 2015 BMW M3 last year, and I'd say I have low experience with car repairs. Those electrical gremlins can be super annoying! My speed readings were going crazy, and I had similar lighting problems. After taking it to my workshop, they found it was just a faulty connection in the wiring harness near the turn signal assembly. The fix was relatively straightforward, they had to replace some corroded connectors and reseat a few plugs. Cost me about 95 Euro and sorted out all the weird electrical issues at once. I'd recommend getting it checked ASAP because electrical problems can sometimes cascade into bigger headaches. Having owned a BMW M3 (and previously an M2), I've learned these things are best dealt with early. Could you share more details about when these issues started and if you notice any pattern (like does it happen more when it's wet or after the car sits for a while)? That might help narrow things down further.

Thanks for sharing your experience! I've got similar symptoms with my M4 (23385 KM on the clock) and just had it serviced last month. Your situation sounds exactly like what I'm experiencing. Super helpful to know it might just be the wiring harness, that's way less scary than what I was imagining! Did you notice if the purple xenon color went back to normal immediately after the fix? Mine started acting up after some heavy rain last week, which makes me think moisture might've gotten in there somewhere. Gonna book it in at the shop tomorrow just to be safe. Rather catch it early than wait for it to get worse. Wonder if this is a common issue with these models? Thanks again for the detailed response, it's really helpful to know what to expect when I take it in.

Hey again! Yeah, I remember dealing with this exact situation. So about those xenon lights, after they fixed the wiring harness on my M3, the purple tint didn't actually go away immediately. It took about two start-ups before they returned to their normal color. The mechanic mentioned this was pretty typical because the system needed to fully reset. And funny you mention the rain, that's exactly what triggered mine too! These BMWs can be a bit sensitive to moisture getting into the wrong places. From my experience owning both the M2 and M3, I've learned these electrical quirks often pop up after wet weather, especially around the headlight assemblies. Quick tip though, when you take it in, make sure they check all the seals around the headlight units too. In my case, they found a tiny gap that was letting moisture seep in. They resealed it while they were fixing the wiring harness, and I haven't had any issues since. The good news is that catching it early like you're doing usually means a simpler fix. Much better than waiting until multiple systems start acting up. Let us know how it goes at the shop, always curious to hear if others run into the same solutions I did!

Thanks for all that detailed follow-up info! You've really put my mind at ease about this whole situation. It's good to know about the two start-ups for the xenon lights to normalize, that'll keep me from panicking if it's not instant. And wow, what a coincidence about the rain being the trigger! I'll definitely make sure to mention the headlight seals when I take it in tomorrow. That's a super helpful tip about the potential moisture entry point, exactly the kind of real-world insight I was hoping for when I posted. I've just started noticing today that the speed sensor warnings seem to show up more when I first start the car, then sometimes clear up after driving for a bit. I'll update the thread once I get it sorted. Really appreciate you taking the time to share your experience, makes me feel a lot better knowing this is probably just a common moisture-related issue rather than something major. Fingers crossed it's just the wiring harness and seals like in your case!