Audi Q8 Diesel: Boost Leak Symptoms Revealed

Had a similar issue with my 2020 Audi Q7 diesel last year. I have some experience working on turbo-related problems, though I usually leave complex diagnostics to professionals. The symptoms you describe match what I experienced, the check engine light, power loss, and that distinctive whistling sound. My pressure sensor was giving false readings due to a loose connection. The workshop found a damaged wire in the connector going to the boost pressure sensor, which was causing erratic signals to the engine management system. The fix was straightforward, they replaced the wiring harness connector and rechecked all related components of the air intake system. Total cost was 95 Euro for parts and labor. Since the repair, the engine has run perfectly with no more boost issues. Before suggesting specific solutions, could you share: Current mileage on your Q8, When did these symptoms first appear, Have you scanned for error codes, Any recent maintenance or repairs, Does the whistling noise change with engine speed This info would help narrow down whether your issue is identical to what I encountered or if it might be something else in the intake manifold system.

My mileage is now at 115813 KM and my latest service was in February. The symptoms started appearing about 2 weeks ago. I did scan for error codes using a basic OBD reader which showed P0299 (Turbocharger underboost) and P0234 (Turbocharger overboost). The whistling noise definitely changes with engine speed, getting louder as RPM increases. When accelerating hard, the hissing becomes quite intense. I have not had any recent repairs done besides regular oil changes. The turbo boost issue seems quite similar to what you experienced. Did your engine also have fluctuating power delivery? I am considering taking it to a workshop but wanted to understand potential causes first, especially since the turbo system is still under warranty. A faulty boost sensor causing these symptoms makes sense, particularly given the error codes. Were there any warning signs before your sensor completely failed?

Thanks for providing those details. Yes, my engine had very similar power delivery issues, it would surge and drop out of nowhere, especially during acceleration. The error codes you are getting are exactly what I saw too. Looking at your situation, this really mirrors my experience with the pressure sensor problem. The key indicator is how the whistling noise changes with engine speed, along with the combination of overboost and underboost codes. The turbocharger is likely getting incorrect signals due to faulty sensor readings. Before my boost pressure sensor completely failed, I noticed: Inconsistent turbo boost under similar driving conditions, The engine light would sometimes flicker before staying on permanently, Gradual increase in fuel consumption over about 3 weeks, Intermittent drop in power, especially during highway merging Since your vehicle is still under warranty, definitely have the dealer check the air intake system and pressure sensor. My repair was relatively simple, but ignoring these symptoms risked damaging the turbocharger itself, which would have been much more expensive. After the sensor and wiring were fixed, my fuel consumption returned to normal, and the engine performance became smooth again. The total diagnostic and repair time was about 3 hours.

Thanks for the comprehensive response. Based on the symptoms and codes matching your experience, I feel more confident now that the pressure sensor might be the root cause. The timing of the issues lines up too, my gradual power loss and increased fuel consumption developed over the past 2 weeks, similar to what you described. I have scheduled an appointment with the dealer for next week. Since the turbo system is under warranty and the symptoms align so closely with your sensor problem, hopefully they can diagnose and fix it quickly. The air intake system and all wiring connections definitely need a thorough check. The changing whistling noise and those specific error codes really seem to point toward sensor issues rather than mechanical turbo damage. This is reassuring, as replacing just the boost pressure sensor and wiring should be relatively straightforward, like in your case. Will update once the dealer checks it out. Hoping for a simple fix like yours, especially since catching it early before any potential damage to the turbocharger itself. Thanks for sharing your experience, it helped clarify what I might be dealing with.