BMW 5 Series Hybrid: Cooling System Crisis and ECU Issues

Hey there! I've got some experience with hybrids and their quirks. Had a similar issue with my 2013 BMW ActiveHybrid 3 (also had a 7 Series before). Those symptoms sound familiar, my car was acting up the same way. Turned out the cable connection to the coolant monitoring system was damaged, causing faulty readings and putting the car in limp mode. The mechanic found corroded wires near the coolant sensor plug. Got it fixed at my regular workshop, they replaced the wiring harness and connections. Cost me around 95 Euro and solved all those warning lights and overheating alerts. Before I can help more specifically: What error codes are you getting? Have you noticed if the leaks are coming from any particular area under the car? This info would help determine if you're dealing with the same issue I had. Let me know these details and I'll try to point you in the right direction!

Thanks for sharing your experience! My car's at 126052 KM and I had my last service about 2 months ago. Been getting P0A7F and P0A9D error codes from my scanner. The leak seems to be coming from the front passenger side, near the coolant reservoir. I initially thought it might be a simple hose issue, but with all these electrical gremlins popping up, your wiring harness story makes a lot of sense. Did you notice any correlation between weather conditions and when the problems would act up? Mine seems worse during cold starts in the morning. Really appreciate any other insights before I head to the shop!

Hey again! Thanks for those details, they're super helpful. I had my ActiveHybrid at almost the same mileage (around 130,000 KM) when I ran into these issues. Those error codes you're getting are exactly what I saw, they're typically related to the hybrid system's cooling circuit. And you know what? I totally noticed the same thing with cold starts! My issues were definitely worse first thing in the morning. The leak location you described matches my experience too, passenger side near the reservoir. Initially, I also thought it was just a simple hose problem, but nope! After my first reply to you, I actually remembered something else that might help. Before getting the wiring fixed, my mechanic found that the corroded connections were causing the cooling system to get confused about the temperature readings. This made the system either overcompensate or not work enough, leading to those leaks from excessive pressure. The weather correlation makes perfect sense because moisture tends to affect those electrical connections more when it's cold. The temperature changes between night and day probably aren't helping either. Quick tip before you head to the shop: Get them to specifically check the wiring around the coolant temperature sensors and the hybrid cooling circuit. My mechanic said these BMWs are known for this issue, and it's often overlooked because everyone jumps straight to thinking it's a mechanical problem. Let me know how it goes at the shop, curious to hear if you've got the same issue I had!

Thanks so much for all this detailed info! You've honestly made me feel a lot better about the whole situation. I was worried I'd be looking at a massive repair bill, but this sounds much more manageable. Your experience with the cold starts and location of the leak matching mine exactly is super reassuring. I'll definitely tell my mechanic to check those wiring connections first, especially around the temperature sensors. It's amazing how something as simple as corroded wires can cause so many problems! Makes total sense about the moisture affecting the connections too, we've had some pretty wild temperature swings lately. I've got an appointment booked for tomorrow morning, and I'll make sure to mention everything you've shared. Really appreciate you taking the time to help me out with this! I'll probably be back to share what they find, might help someone else with the same issue down the line. Thanks again for walking me through your experience, it's been super helpful!