Audi A2 Temperature Sensor Woes Affect Multiple Systems

Had the exact same symptoms on my 2004 Audi A3 1.4 TSI last summer. As someone with moderate experience working on cars, I first thought it was just a temperature sensor issue too, but it turned out to be more complex. After multiple diagnostic attempts, my workshop found the AC control unit itself was defective, not just the sensors. The temperature gauge was showing incorrect readings because the control unit wasnt properly processing the sensor inputs. The repair involved: Complete diagnostic scan, Testing all temperature sensors, Replacing the AC control unit, Full sensor calibration of the new unit Total cost was 980 Euro including parts and labor. The sensor calibration after installing the new control unit was crucial, without it, the system wouldnt work properly. Could you share: Any specific error codes youre getting? Does the AC fan turn on at all? Are your temperature readings fluctuating or completely dead? Have you noticed any coolant leaks? This info would help determine if youre dealing with the same root cause I had.

Last service was done at 103000 KM, only 122 KM ago. After checking the repair manual, the heat exchanger temperature sensor replacement requires special calibration tools. The HVAC system diagnosis also showed the compressor engages but no cold air flows. Getting P0128 and P0115 error codes which point to sensor malfunction rather than a control unit issue. Good suggestion about checking for coolant leaks though, will inspect the engine cooling system connections before going further. Multiple sensors communicate with the climate control on these models. Temperature readings are inconsistent, jumping between -10C and +40C out of nowhere. Fan works normally on all speeds which suggests the blower motor and basic controls are functioning correctly.

Good to hear back and thanks for those details. Your symptoms actually differ from what I experienced on my A3. While I had control unit failure, your P0128 and P0115 codes combined with those erratic temperature readings (-10C to +40C) strongly suggest a sensor malfunction rather than a full control unit issue. The cooling system connection check is smart, when I dealt with sensor issues previously, a small coolant leak near the heat exchanger caused similar temperature reading fluctuations. The fact your compressor engages but produces no cold air matches typical temperature sensor failure patterns in these models. Since vehicle maintenance records show recent service, the sensor likely failed prematurely. One crucial point about the calibration, my workshop had to order specific tools for the heat exchanger sensor adjustment. They initially tried without proper calibration which only created more issues. A full diagnosis should verify: Coolant level and pressure, All cooling system connections, Sensor wiring integrity, Heat exchanger physical condition Would be interested to know what you find during the coolant leak inspection. Based on similar cases, sensor replacement with proper calibration should resolve these symptoms.

Thanks for the detailed follow-up. The coolant leak inspection revealed nothing obvious, but I noticed the wiring harness near the heat exchanger looks worn. This could explain the erratic temperature sensor readings affecting the HVAC system performance. Going to book it in next week and request they specifically check the wiring before replacing any parts. Will make sure they have the required calibration tools for the heat exchanger temperature sensor replacement if needed. The cooling system pressure test will also be worth doing since intermittent issues can be hard to spot visually. The consistent P0128 and P0115 codes plus those fluctuating temperature readings between -10C and +40C really do point to sensor issues rather than control unit problems. Good to rule out the more expensive repairs first. The fact that basic fan operation works normally also supports this diagnosis path.