BMW 4 Diesel: HVAC System Failures & Error Code Alert

I had a similar issue with my 2017 BMW 3 diesel last winter. The symptoms were nearly identical, weak heating performance and control system warnings. Turned out the wiring harness connecting to the blend door actuator was damaged, causing intermittent connection issues. My mechanic found several frayed wires where the cable bundle flexes near the firewall. They had to replace the entire harness assembly as the individual wires couldn't be reliably repaired. The job took about 4 hours to complete. This was actually a significant issue because leaving it unfixed could have led to complete heating system failure and potential electrical problems. I'd strongly recommend getting it checked soon, as winter weather really exposes these kinds of faults. Based on your symptoms, I'd bet you're dealing with something similar rather than a solar sensor issue. The error code should help pinpoint it. Make sure whoever works on it checks the wiring connections first before replacing any sensors or modules.

Thanks for sharing your experience with the wiring harness, it's really helpful to know what to look out for. Do you remember roughly how much you ended up paying for the whole repair? Also curious if you've had any other heating or electrical issues pop up since getting it fixed?

Hey there! Actually, I need to correct my previous assumption, it did turn out to be the solar sensor after all! I just got back from my mechanic last week and they found the issue was a faulty connection between the sensor and its plug. Once they fixed that cable connection, all the heating problems disappeared like magic. The total bill came to 95 €, much less scary than the wiring harness repair I was worried about initially! And to answer your other question, nope, haven't had a single heating or electrical problem since the fix. The AC control system is working perfectly now too. I'm honestly relieved it wasn't something more serious like I first thought. Sometimes the simplest solution is the right one! Just goes to show how one loose connection can cause such annoying symptoms. If your symptoms are similar, definitely get your solar sensor connections checked first before looking into more complex issues.

Just got back from the mechanic and you were spot on! Took my car in yesterday and they diagnosed the same issue, a faulty solar sensor connection. What a relief it wasn't anything major. My mechanic fixed it in about an hour, and the total cost was pretty reasonable, just around 100 bucks including labor. The best part is my heating system is working perfectly now. The AC controls are back to normal too, and that annoying error code has disappeared. It's amazing how such a small part can cause so much trouble! Really glad I asked here before assuming the worst. Thanks again for helping me avoid an unnecessary expensive repair. This experience has definitely restored some of my faith in finding honest mechanics who don't try to oversell repairs. Guess I'll know what to check first if this ever happens again. Time to enjoy my properly functioning heating system!