Audi S1 Cooling System Failures Point to Bad Sensor

Having dealt with a similar situation on my 2012 Audi A1, I can share some relevant experience from working with HVAC system issues. As someone with moderate experience in car maintenance, this particular problem required professional intervention. The symptoms you describe align closely with what I encountered, multiple cooling system faults and AC malfunction. In my case, the root cause was indeed a defective air conditioning control unit, which was affecting the entire HVAC system operation and sensor readings. The workshop performed these key steps: Full diagnostic scan, Temperature sensor calibration check, Control unit testing, Inspection for potential coolant leak, Complete HVAC system pressure test The repair involved replacing the control unit and recalibrating all connected sensors. Total cost was 980 Euro, including parts and labor. The fix resolved all warning messages and restored proper AC function. To provide more specific guidance for your S1, could you share: Current mileage, When the problems first appeared, Whether any recent maintenance was performed, If you notice any unusual sounds from the AC system, Whether coolant levels remain stable This information would help determine if your issue is identical to what I experienced or if additional factors need consideration.

Last service was completed at 102783 KM with a full inspection of the engine cooling system. After reading your detailed response, I suspect my issue might be different. The temperature gauge shows normal readings when the engine is cold, but fluctuates once warmed up. The coolant level has remained stable with no visible leaks, and I havent noticed any unusual sounds from the AC components. My workshop initially suggested a complete heat exchanger replacement without proper diagnostics, which seemed excessive. Based on your experience, I agree a full diagnostic scan should be the first step before any parts replacement. Would you recommend checking the wiring connections to the temperature sensors before proceeding with more extensive repairs?

Based on the symptoms you describe, especially the fluctuating temperature readings when warm, checking the wiring connections is definitely a smart first step. When I encountered similar issues with my A1, the diagnostic scan revealed intermittent sensor signals that initially pointed to a heat exchanger problem. My mechanic found corroded wiring connections at the temperature sensor, causing unreliable readings to the engine cooling system. This triggered the error codes and disabled the AC as a precaution. The sensor malfunction created similar temperature gauge fluctuations to what youre experiencing. The fix in my case was much simpler and cost-effective than a full heat exchanger replacement: Cleaned corroded terminals, Replaced damaged wiring section, Updated sensor calibration, Cleared fault codes Total repair cost was 180 Euro including labor. Given your stable coolant levels and normal cold readings, Id strongly recommend insisting on: 1. Complete wiring inspection 2. Temperature sensor testing 3. Heat exchanger pressure test 4. Full diagnostic scan This systematic approach helped avoid unnecessary parts replacement in my case and might save you significant repair costs. Have you noticed if the temperature fluctuations follow any specific pattern or occur at particular engine speeds?

Thank you for providing that insight. The temperature fluctuations typically occur when the engine reaches normal operating temperature, usually after about 15 minutes of driving, regardless of engine speed. Based on your systematic troubleshooting approach, I will insist on having the full diagnostic process before authorizing any parts replacement. I just checked the wiring myself and noticed some discoloration near the temperature sensor connector, which seems to support your theory about potential connection issues. The heat exchanger itself shows no visible damage or leaks, making me more confident that the sensor or wiring could be the root cause rather than a complete unit failure. I will schedule an appointment with my workshop and specifically request the diagnostic steps you outlined, particularly the temperature sensor testing and wiring inspection. The 180 Euro repair cost you mentioned is much more reasonable than the quoted heat exchanger replacement. Will update once I have the diagnostic results.