RS6 Coolant Loss: Critical Warning Signs & Solutions

Had a similar issue with my 2019 RS4 last winter. Have some experience with basic maintenance and repairs. The coolant leak symptoms started just like yours, warning lights and low coolant level. After checking, found it was a faulty wiring connection to the coolant level sensor. The cooling fan was working fine and there was no actual leak in the system. Took it to a workshop where they diagnosed a damaged connector plug. They replaced the wiring harness and connections to the sensor for 95 Euro. Pretty straightforward fix, much better than initially feared water pump failure or serious engine overheating issues. Before jumping to conclusions about major repairs, would recommend checking: Are you seeing any radiator fluid under the car? What specific error codes are you getting? Has the engine temperature gauge shown any unusual readings? Have you noticed any sweet smell from the engine bay? Could you share the specific error codes? That would help narrow down if your issue is similar to what I experienced or if it might be something different. Also suggest checking the coolant level when the engine is cold for an accurate reading. If it keeps dropping rapidly, might point to an actual leak rather than a sensor issue.

Thanks for sharing your experience. Mine has 79994 KM and the latest service was just 2 months ago. Checked under the car and noticed small puddles near the radiator hoses area. Engine temp stays normal but coolant level keeps dropping steadily. Getting error code P2181. The sweet smell is definitely there when parking after a drive. Starting to think its more than just a sensor issue. No white smoke from exhaust though, which is good news as it likely rules out a head gasket problem. Going to book it in next week, but trying to understand if anyone had similar symptoms that turned out to be a water pump failure? Really hoping its just a loose radiator cap or worn hose rather than something major. Looking forward to hearing from others who might have dealt with similar cooling system problems.

Thanks for the additional details, seeing the coolant puddles and sweet smell with error code P2181 definitely points to a physical leak rather than the sensor issue I had. Got the exact symptoms on my RS4 about 6 months after my sensor fix. The radiator cap seemed fine, but the main issue was a hairline crack in one of the radiator hoses where it connects to the water pump. The cooling fan was working properly but couldnt compensate for the constant coolant loss. The repair involved: New radiator hoses, System flush to remove air pockets, Fresh coolant refill, Pressure testing the whole system Total cost was around 450 Euro for parts and labor. Much better than a full water pump replacement which was my initial worry. Quick tip: While waiting for the repair appointment, keep checking the coolant reservoir level daily. Top up if needed but dont overfill, just maintain it at the minimum mark to avoid engine damage. Also worth carrying some spare coolant in case of emergency. Did you notice if the leak gets worse after the engine has been running for a while? This could help pinpoint if its a pressure-related issue versus a simple connection problem.

Based on the conversation history, I would respond from's perspective: Thanks for the detailed feedback. Yes, the leak definitely gets worse after longer drives, especially noticeable after 30 minutes of running. The coolant reservoir level drops faster during highway driving compared to city use. Just did another check and noticed the puddles are slightly larger now. Managed to trace the leak more precisely, seems to be coming from the area where the hose meets the water pump housing. Your experience with the cracked hose sounds very similar to what Im seeing. Will definitely keep monitoring the coolant level daily and stock up on some extra coolant before the appointment. The cooling fan seems to run normally and engine temperature stays stable as long as I maintain the coolant level. Good to know about the repair costs and process. Really hoping its just the hose connection like in your case. Will update once I get it properly diagnosed and fixed. Thanks for all the useful information about the cooling system repairs.