Q7 System Failures Point to Faulty Fog Sensor

As someone with some automotive repair experience, I had a similar situation with a 2017 Q8 where multiple systems started showing dashboard warnings. The symptoms were nearly identical, especially the sensor malfunction affecting climate control and visibility systems. After initial diagnosis, it turned out the main wiring harness connector to the central control module was corroded, causing various automotive sensor failures. The connection issue was affecting multiple systems simultaneously, which explains why seemingly unrelated functions were malfunctioning at once. The repair involved cleaning the connector pins and replacing a damaged portion of the wiring. Total cost was 95 Euro for parts and labor, which was reasonable considering the scope of the problem. Since the fix, all systems have worked flawlessly, including the windshield fogging prevention and temperature controls. To better assist with your specific case, could you share: Are there any specific error codes stored? When did these issues first appear? Have you noticed any correlation with weather conditions? Does the issue persist after the engine warms up? These details would help determine if your Q7 is experiencing the same root cause as my case.

Last service was completed at 8123 KM, and since then an electrical issue has persisted despite the maintenance. Thanks for the detailed response about the wiring harness. The error codes are P0113 and P0118, which appeared shortly after a period of heavy rain. The dashboard warning lights come on intermittently, usually during cold starts, and the malfunction continues even after warm-up. The AC system remains completely unresponsive regardless of outside temperature. Looking at the workshop manual, these codes point to temperature sensor circuit problems, but my concern is whether this could be part of a larger electrical system failure. The timing of multiple system failures seems too coincidental to be separate issues.

Thanks for providing those error codes and additional details. Your symptoms match almost exactly what I experienced with my Q8, especially the timing after rainfall and the connection to temperature sensor circuits. The P0113 and P0118 codes typically indicate intake air temperature and engine coolant temperature sensor issues, but in my case, these were secondary symptoms of the corroded wiring harness. The water intrusion from heavy rain likely accelerated the corrosion process, similar to your situation. After my repair, the workshop found moisture had seeped into the main connector housing, creating resistance in the circuit. This explained why the automotive sensor readings were inconsistent and why multiple systems were affected simultaneously. The sensor calibration was impossible until the wiring issue was resolved. One telling sign was that the dashboard warning indicators would appear out of nowhere during cold starts. This matches your experience and further suggests a wiring connection problem rather than individual sensor failures. Since your vehicle has relatively low mileage, this repair might even be covered under warranty. The wiring harness replacement in my case prevented further system malfunctions and resolved all the temperature-related issues, including the AC and defrost functions.

The malfunctions you described match my situation perfectly, especially about the dashboard warning lights during cold starts. What you mentioned about water intrusion makes a lot of sense given the timing after that rainy period. I'll definitely have them check the wiring harness connectors when I take it in. The humidity sensor problems and connected climate control issues sound identical to what I'm experiencing. Having the error codes point to temperature circuits while multiple systems are failing does suggest a central wiring issue rather than individual sensor problems. I'm relieved the repair cost was reasonable in your case. Will schedule service next week to have them inspect the wiring and check for moisture damage. The car sensor malfunctions and intermittent nature of the problems have been frustrating, but at least there seems to be a clear path forward for diagnosis and repair. Thanks for sharing your experience, it helped narrow down the likely cause.