SQ8 TDI Turbo Issues: Multiple Red Flags Emerge

Had a very similar issue on my 2017 Q7 TDI last winter. Having some experience with turbo system problems, I recognized those symptoms immediately, especially the whistling noise and power loss during acceleration. The engine light came on and diagnostic initially suggested boost pressure sensor issues, just like yours. After bringing it to the workshop, they found a loose electrical connection at the boost pressure sensor plug. The cable had worked itself loose over time, causing erratic boost pressure readings and the ECU to reduce power as a safety measure. Total repair cost was 95 Euro including diagnostic and fixing the connection. The job took about an hour since they had to verify proper sensor operation after the repair. Before jumping to replace parts, definitely have the wiring and connections checked thoroughly. A boost leak test would also be worthwhile to rule out any air intake system issues. Could you share: Current mileage on your SQ8? Any recent work done on the turbocharger or intake system? Are these symptoms constant or do they vary with weather conditions? Have you noticed any exhaust smoke? This info would help determine if your issue matches what I experienced or if it might be something else in the turbo system.

Latest service completed at 112067KM and the symptoms started shortly after. After checking based on suggestions, I noticed oil residue near the turbocharger connection points. The hissing sound is most noticeable under the intake manifold area. The symptoms are constant regardless of weather conditions, with no visible exhaust smoke. A boost leak test might make sense as the next step, since the turbo boost problems seem to be getting worse. The pressure sensor readings are erratic according to my OBD scanner, fluctuating between normal and extremely low values during acceleration. No previous work has been done on the turbocharger or intake system. Running fine until the recent issues started showing up.

After seeing your update about the oil residue and location of the hissing sound, I am now confident your issue differs from my electrical connection problem, despite the similar symptoms. The oil residue near the turbo connections combined with the erratic pressure sensor readings points toward a potential boost leak from degraded seals or cracked hoses. My initial assumption about the boost pressure sensor being the primary issue was likely incorrect. When my turbo system showed similar symptoms, I also used an OBD scanner and saw fluctuating readings. However, the key difference is the oil residue you found, which I never experienced with my sensor connection issue. The constant nature of your symptoms, regardless of weather, and the worsening turbo boost problems suggest a mechanical rather than electrical fault. The check engine light in your case is likely triggered by the inconsistent boost readings caused by the leak, rather than a faulty sensor itself. Recommend getting a pressure test done specifically focusing on the area where you spotted the oil residue. Based on the service history you shared, the turbo seals might need replacement. This would explain the combination of symptoms, the hissing, power loss, and erratic sensor readings. The repair cost will likely be higher than my 95 Euro connector fix, but addressing it promptly will prevent potential damage to other engine components.

Thanks for the detailed input. Just wanted to update that I took the car to a workshop today for a proper diagnosis. You were right about the boost leak, they found a cracked hose connection between the turbocharger and intake manifold, plus worn seals causing the oil leak I spotted. The check engine light and erratic pressure sensor readings were indeed symptoms of the leak, not a faulty sensor. The boost pressure sensor itself tested fine once they fixed the leaks. Total repair cost came to 485 Euro including new seals, hose, labor, and testing. The turbo system is now working perfectly, no more hissing sounds, power is back to normal, and fuel consumption has improved. Really glad I got this checked before any serious damage occurred to the turbocharger. Will definitely keep a closer eye on the intake system components during future services. Thanks again for helping me understand what to look for and saving me from unnecessarily replacing the pressure sensor.