BMW 1 Series: Coolant Warning + Check Engine Issues?

Hey there! I've got some experience with BMWs and can relate to your issue. I had something similar happen with my 2012 BMW 3 Series diesel. The symptoms were exactly the same as what you're describing. Took it to my regular workshop, and it turned out to be a faulty wiring connection to the coolant temperature sensor. Fixed it for about 95 Euro, basically, they had to replace some corroded wiring and reconnect the sensor properly. The whole thing took a couple of hours to sort out. Before jumping to conclusions though, could you share what model of 1 Series you have (116d, 118d, etc.)? Also, have you noticed any coolant leaks or had to top up the coolant recently? This info would help me give you more specific advice based on my experience. Side note, if you're interested, the 5 Series from the same period had similar issues too.

Yes, I've got a 118d with 185041 KM on the clock, and my last service was about 2 months ago. I've noticed I need to top up the coolant more frequently lately, maybe every couple of weeks. I'll check under the car tomorrow morning for any obvious leaks, but haven't spotted anything major in my driveway yet. The coolant warning usually shows up after driving for about 15-20 minutes, especially during longer trips. Thanks for the tip about the wiring, I'll definitely get that checked along with the sensor connections.

Oh, that additional info really rings a bell! My 2012 320d had the exact same symptoms when it was around 180,000 KM. When you mentioned having to top up the coolant frequently, that's what happened to me too. Initially, I thought it was just the sensor wiring like I mentioned before, but it turned out I had a slow leak from the water pump gasket. These things can be tricky because the leak might not be obvious right away, the coolant can evaporate before it hits the ground. In my case, I kept topping up the coolant every few weeks, just like you, until I finally got it properly checked. The mechanic found that the water pump gasket had deteriorated over time. They ended up replacing the whole water pump assembly since these parts tend to wear out around this mileage anyway. It solved both the coolant loss and the warning lights. Since you're dealing with similar symptoms in a similar engine (the 118d and 320d share quite a few components), I'd definitely recommend getting the water pump area checked. My repair ended up costing more than just fixing wiring, but it was worth it to solve the problem properly. Better safe than sorry with these engines, right? Let me know what you find out, I'm curious if your issue turns out to be similar to what I experienced!

Thanks so much for sharing your experience! After reading about your water pump issue, I did some more checking this morning. You're absolutely right, I found some dried coolant residue around the water pump area that I hadn't noticed before. I've booked it in at my mechanic's for next week. They quoted me roughly 500 for a complete water pump replacement, which sounds about right based on what you paid. Really glad you mentioned this because I was just about to get the wiring checked first, but now I can tell them to focus on the water pump area right away. These BMWs might be great to drive, but they sure know how to keep us on our toes with maintenance! I'll update the thread once I get it sorted, might help others with similar issues down the line.