BMW 7 Series Overheating + Limp Mode: Coolant Crisis Help

Hey there! I had similar issues with my 2003 BMW 5 series last year. The symptoms were almost identical, overheating, limp mode, and coolant puddles. After two visits to the garage, they found that the main culprit was a damaged wiring harness to the coolant pump control module. The constant engine heat had degraded the insulation, causing intermittent communication failures. The coolant leak in my case came from a cracked expansion tank, which was a secondary issue caused by the system overheating. This was actually pretty serious since continuous overheating could've led to engine damage if not addressed quickly. They had to replace the wiring harness, connectors, and the expansion tank. Once fixed, all warning lights cleared up and the car's been running perfectly since then. Make sure whoever checks your car looks specifically at the wiring connections to the cooling system components, these issues aren't always obvious during a basic inspection. Hope this helps with your diagnosis.

Thanks so much for sharing this! That's super helpful as it sounds exactly like what I'm dealing with. I'm curious, do you remember roughly how much you ended up paying for the whole repair job? Also, has everything been running smoothly since then, or have you noticed any other cooling system issues pop up?

Hey again! Happy to give you a follow-up! I just got my car back from the mechanic last week, and you'll be glad to hear they fixed that pesky control unit communication error. Turned out it was exactly what I'd suspected, just a faulty cable connection to the cooling system module. Total bill came to 95€ for the repair, which honestly wasn't as bad as I was expecting! And since you asked, everything's been running like a dream since the fix. No more warning lights, no more overheating issues, and most importantly, no more stress about whether my car's going to act up! The engine's running at normal temps again, and I haven't seen a single drop of coolant on my garage floor. Looking back, getting that wiring connection sorted was definitely the right call. It's amazing how such a small issue can cause so many scary symptoms, right? If you end up getting yours fixed, let me know how it goes. Always good to compare notes with fellow BMW owners!

Thanks for the detailed update! Really glad I asked here before spending a fortune. Just got back from my trusted mechanic today, you were spot on about the wiring being the main issue. Had some frayed connections causing all those problems. My repair was a bit more expensive since they also found a small crack in the coolant reservoir, but still way less than I feared. The whole thing cost about €400 including parts and labor. Car's running beautifully now, no more warning lights, no leaks, and temperature's staying steady where it should be. Funny how a bad wire can cause such a headache! Really appreciate everyone's help here, especially your experience with the same problem. Saved me from getting ripped off at that first place that wanted to replace half the cooling system. Nothing beats getting advice from people who've actually dealt with these issues firsthand!