SQ8 TDI Turbo Troubles: Power Loss and Whistling Sound

Having some experience with turbo systems, I encountered a similar issue on my 2017 Q7 TDI V8. The symptoms you describe match exactly what I experienced, particularly the whistling sound and increased fuel consumption. The turbocharger system on these engines is quite complex, and in my case, the electrical bypass valve was causing inconsistent boost pressure. The turbo actuator was receiving incorrect signals, leading to the exact symptoms you mention. My workshop diagnosed it using pressure testing of the turbo system and electronic diagnostics of the boost pressure control circuit. The repair involved replacing the electrical bypass valve, which resolved all symptoms including the stalling and power loss. The total repair cost was 250 Euro, including parts and labor. After the fix, fuel consumption returned to normal and the engine ran smoothly again. Before suggesting specific solutions, it would help to know: Current mileage on your SQ8, Whether you notice the issues more during cold starts or when the engine is warm, If you hear the whistling sound at specific RPM ranges, Any recent maintenance history, especially related to the turbocharger components These details would help determine if your issue matches the common turbo actuator failures these engines sometimes experience.

Latest service was at 163000 KM. The whistling sound occurs mainly when engine is warm, around 2000-2500 RPM. Running diagnostics showed fault code P0299 related to turbo underboost. The turbo wastegate seems to be the prime suspect based on the symptoms and error codes.

Thanks for the additional details about your SQ8. The P0299 code combined with the whistling sound at 2000-2500 RPM matches what I experienced with my Q7 precisely. As I mentioned earlier, my turbo actuator valve issue presented similar symptoms. After having resolved my issue, I can confirm that an underboost condition often points to either a failing wastegate or turbo actuator. In my case, the electrical bypass valve was the root cause, but given your fault code and rpm-specific symptoms, the wastegate mechanism seems the more likely culprit. Since fixing the turbo system on my vehicle, I have learned that boost pressure sensor readings during acceleration can help pinpoint whether its a wastegate or actuator problem. With your specific symptoms occurring at 2000-2500 RPM, this strongly suggests a mechanical rather than electrical issue with the boost control. The repair cost might be higher than what I paid (250 Euro) if the wastegate requires replacement rather than just the actuator valve I needed. Before proceeding with repairs, request a complete pressure test of the turbo system to rule out any boost leaks, as these can mimic wastegate failures. Have you noticed if the whistling gets louder as ambient temperatures increase? This could help confirm the wastegate diagnosis.

Based on all the information shared, I believe I have enough to proceed with repairs. The wastegate seems to be the most likely cause, especially given the P0299 fault code and the specific RPM range where the whistling occurs. The turbo actuator symptoms from the other case match mine closely, but the diagnostics point more toward the wastegate as the root issue. The boost pressure loss at 2000-2500 RPM is particularly telling, and combined with the increased fuel consumption and power loss, it creates a clear pattern. Will schedule the repair soon and request a complete pressure test of the turbocharger system first, then proceed with the wastegate replacement if confirmed. The cost will likely be higher than a simple actuator valve replacement, but fixing it properly now should prevent more expensive repairs later. Thanks for sharing your repair experience. The similarities in symptoms were helpful in narrowing down the problem, even though my issue appears to be mechanical rather than electrical. Will update once the repair is complete in case others encounter similar boost pressure problems with their V8 TDI.