RSQ3 Coolant Issues Trigger Check Engine Warning

I had a similar issue with my 2019 RS3 and can share some insights based on my experience with cooling system troubles. Like yours, my check engine light kept coming on while the coolant level was dropping. After checking the vehicle at my workshop, they found a faulty connector at the coolant temperature sensor was causing incorrect readings. The bad connection was making the system think there were cooling issues, triggering the check engine light and affecting coolant circulation. Total repair cost was 95 Euro for replacing the wiring connector and clearing the system. This seems to be a known weak point in these engines. Before the fix, I was also concerned about a potential coolant leak or failing water pump, but those components were fine. The real culprit was much simpler. To help diagnose your specific case, could you share: Are you noticing any engine overheating? Is there visible coolant under the car? How quickly does the coolant level drop? Have you noticed any air pockets in the cooling system? What exact error code are you getting? With these details, I can provide more targeted advice based on my experience with a very similar engine setup.

Thanks for the troubleshooting suggestions. My last service was at 185000 KM and the error code reads P2181. The coolant drops about 1cm every 2 weeks but I see no visible leaks or puddles. The temperature gauge stays normal and the cooling fan seems to run at regular intervals. A pressure test might help locate if theres a slow coolant leak somewhere in the system. I will check those sensor connections you mentioned before assuming its a major water pump or head gasket issue.

Thanks for those additional details. This definitely sounds familiar to what my RS3 was showing before the fix. The P2181 code typically points to cooling system performance issues, and your symptoms mirror my experience almost exactly, slow coolant loss without visible leaks. The fact your cooling fan operates normally and engine temperature stays stable is actually good news. In my case, these were also normal despite the sensor connector issue. Before replacing any major components, have your workshop check the coolant reservoir cap and all sensor connections around the cooling system. A faulty radiator cap can cause slow coolant loss without visible leaks. My engine was also around that mileage when these issues started. The pressure test is a smart next step, wish I had done that first before worrying about the water pump. If the pressure test shows no leaks, focus on the electrical connections to the cooling system sensors. One tip from my experience: when they check the sensor connections, make sure they inspect the entire wiring harness near the coolant temperature sensors. These wires can develop micro-cracks that are hard to spot but cause intermittent connection issues. Would you mind checking if your coolant loss rate increases when the engine runs at higher RPMs? This detail helped pinpoint my issue.

No leaks underneath and steady temperature readings do bring some relief. Checked the RPMs as suggested and coolant loss seems consistent regardless of engine load. Will go ahead with the pressure test first and have them inspect those electrical connections around the coolant reservoir and temperature sensors. The wiring harness inspection tip could save me from unnecessarily replacing major cooling system parts. At least now I have a clear starting point and know what to ask the workshop to check. Nice to hear someone else solved a similar issue without needing an expensive water pump replacement. Will update once I get the pressure test results and have those connections checked. Thanks for walking me through the diagnostic steps.