BMW 4 Coolant Warning + Check Engine: What's Going On?

I had a similar issue with my 2011 BMW 3 series (coming from a mechanic with some experience working on cars). Started with the same warning lights, and I initially thought it was just low coolant too. Turned out the temperature sensor's wiring connection was faulty. My regular workshop checked it and found that the plug connection to the sensor was corroded and making poor contact. The fix wasn't too complex, they cleaned and reseated the connection, replaced some damaged wiring, and everything went back to normal. Total bill was around 95 Euro, which wasn't too bad considering the headache it was causing. To help you better, could you share: Are you noticing any actual cooling issues or overheating? Have you checked the coolant level yourself? Does the problem happen more when the engine is cold or warm? By the way, I also own a BMW 5 series now, and these models can be quite similar in their cooling systems.

Thanks for sharing your experience! My car has 151702 KM on it and was last serviced 3 months ago. I actually checked the coolant level, and while it's slightly low, it doesn't seem low enough to trigger these warnings. The issue mostly occurs when the engine is warm, usually after about 15-20 minutes of driving. Haven't noticed any actual overheating yet, but I'm being cautious and keeping an eye on the temperature gauge. Your sensor wiring issue sounds pretty similar to what I might be experiencing. I'll definitely have my mechanic check the connections when I take it in next week.

Hey again! Wow, after hearing those additional details about your situation, it really does sound similar to what I dealt with. Since I mentioned my experience with both the 3 and 5 series BMWs, I can tell you that when my 3 series had this issue, it also started acting up mainly when warm, just like yours. The fact that you're seeing this happen after 15-20 minutes of driving, combined with the coolant level being only slightly low, makes me even more convinced it could be electrical. When I had the wiring issue, my coolant level was also just a tad low, but that wasn't the real problem. One thing I didn't mention in my first reply, before I got it fixed, I noticed the temperature readings would sometimes fluctuate out of nowhere, which was a pretty good indicator that it was an electrical issue rather than an actual cooling problem. Did you notice anything like that? Since your car has 151702 KM on it, it's in that sweet spot where these kinds of electrical gremlins tend to show up. Mine had similar mileage when it happened. Definitely have your mechanic check those sensor connections first before diving into more complex (and expensive) repairs. Let us know what your mechanic finds, I'm really curious to see if it turns out to be the same issue I had!

Thanks for that detailed follow-up! Actually, yes, now that you mention it, I have noticed some weird fluctuations in the temperature readings. Sometimes it seems to jump around a bit, which was making me nervous, but what you're saying about electrical issues makes a lot of sense. It's really helpful to hear from someone who's dealt with these BMW quirks before. I've got the appointment scheduled for next week, and I'll definitely have them look at those sensor connections first. You've saved me a lot of worry, I was imagining worst-case scenarios about the entire cooling system needing replacement! The fact that your repair bill was reasonable is also really encouraging. I'll update this thread once I get it checked out. Thanks again for taking the time to share your experience, it's been super helpful in narrowing down what might be going on with my car!