A8 Temperature Gauge Issues Point to Cooling System Fault

I had a very similar issue with my 2009 Audi A6 4.2L. With some experience working on cars, I can tell you that inconsistent temperature readings often point to electrical issues rather than actual cooling system problems. In my case, the problem turned out to be a blown fuse controlling the temperature sensors. The symptoms matched yours exactly, erratic temperature gauge, slow warm-up times, and check engine light. I initially thought it was a radiator blockage or cooling grille issue, but the automotive cooling system itself was perfectly fine. The workshop diagnosed it quickly with their diagnostic tool. The repair was straightforward, just a fuse replacement, costing 52 Euro including labor. The engine has been running at normal temperatures since then. Before jumping to conclusions about cooling system components, could you share: Are you getting any specific error codes? Does the temperature fluctuate more during city driving or highway speeds? When did you last have your cooling system serviced? Have you noticed any coolant leaks or low coolant levels? This information would help determine if youre dealing with a similar electrical issue or something else in the cooling system.

Thanks for sharing your experience. My mileage is currently at 86632 KM, and the last major service was done about 4000 KM ago where they performed a standard inspection but found no issues with the thermal management system. The error code reader shows P0116 (Engine Coolant Temperature Circuit Range/Performance Problem). The temperature fluctuations seem worse during city driving. The engine cooling system maintains more stable readings on highways, though still not completely normal. No visible coolant leaks, and the level has remained consistent since the last service. After reading your response, I will have the electrical components checked first before investigating potential radiator blockage issues. The engine overheating symptoms being worse in city traffic does make me wonder if its more than just a fuse though. Can you share what diagnostic tool your workshop used? Would help to mention this when I take it in.

Thanks for providing those details. After fixing my initial fuse issue, I actually encountered the same P0116 code a few months later. The steady coolant level and worse symptoms during city driving mirror what I experienced too. In my follow-up repair, the workshop found the engine coolant temperature sensor itself was faulty, not just the fuse. The thermal management system relies heavily on accurate sensor readings, and a failing sensor can cause exactly these symptoms, inconsistent readings and poor engine cooling performance. The diagnostic tool used was a VCDS (VAG-COM Diagnostic System). Most Audi workshops should have this or equivalent professional diagnostic equipment that can properly read all the sensor data from the engine cooling system. The sensor replacement cost was around 180 Euro including labor. After the repair, the temperature readings stabilized, the check engine light went off, and warm-up times returned to normal. No more fluctuations whether in city traffic or highway driving. A few things to check before your workshop visit: Have them test the coolant temperature sensor resistance, Check the wiring harness for any damage, Verify the cooling grille actuator is functioning correctly, Make sure the radiator blockage isnt internal scaling The P0116 code specifically points to the temperature circuit, which makes me confident youre dealing with a sensor issue rather than a mechanical cooling system problem.

Thanks for the detailed information about the VCDS. I scheduled an appointment with a certified workshop, and I will specifically request they check the coolant temperature sensor and circuit given the P0116 code. Makes sense that city driving would strain a faulty sensor system more. The suggestion about checking the wiring harness is particularly helpful since my car has been parked outdoors through some harsh weather. Engine overheating concerns had me worried about expensive repairs, but a sensor issue sounds much more manageable. One last question about your repair, did you notice any immediate improvement in fuel consumption after fixing the sensor? I realize now that my fuel economy has gradually gotten worse, likely due to the engine running rich from incorrect temperature readings. Will update the thread once I get the diagnostic results. If anyone else runs into similar car overheating symptoms with a P0116 code, this discussion should help point them in the right direction for repairs.