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2021 S5 3.0T Turbo Whine/Rattle and Reduced Boost

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David L. · rep 0 · May 22, 4:24 AM · 1 replies · solved · Question

Vehicle: 2021 Audi S5 3.0T Coupe

Hey everyone,

I've got a 2021 Audi S5 3.0T Coupe with about 35,000 miles, and I've started noticing a distinct whining sound from the engine bay, especially under acceleration. It's not a supercharger whine, but more of a high-pitched turbo whine. Along with that, I feel like the car isn't pulling as hard as it used to, almost like there's reduced boost.

Sometimes, when I let off the throttle, I also hear a slight rattling sound, which makes me think it might be related to the wastegate. The check engine light hasn't come on yet, but the performance drop is definitely noticeable.

Is this a common issue with the B9.5 S5's 3.0T engine? What should I be looking for or asking the dealer to check?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:24 AM

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ClearTheCode admin answer:

The symptoms you're describing—a distinct turbo whine, reduced boost, and a rattling sound on throttle lift-off—are strong indicators of an issue with the turbocharger system in your 2021 Audi S5 3.0T. While the 3.0T in the B9.5 generation uses a single twin-scroll turbocharger (not a supercharger like older 3.0T models), these components can still develop issues.

Common Causes & Diagnostics:

  1. Turbocharger Bearing Wear: A high-pitched whine often signals wear in the turbocharger's internal bearings. As the bearings wear, the turbine shaft can develop play, leading to noise and reduced efficiency.
  2. Wastegate Actuator/Flapper Issues: The rattling sound you hear on throttle lift-off is very characteristic of a loose or failing wastegate flapper or its actuator. If the wastegate isn't sealing properly, boost pressure can leak, leading to reduced power and the 'reduced boost' feeling.
  3. Boost Leaks: A crack in an intercooler pipe, a loose clamp, or a damaged diverter valve can cause boost pressure to escape, resulting in a whine and noticeable power loss. This might not always trigger a CEL immediately.
  4. Turbocharger Inlet/Outlet Issues: Obstructions or damage to the air intake or charge pipes leading to/from the turbo can also affect performance and create unusual noises.

When to See a Shop:

  • Promptly: While a CEL might not be on yet, reduced boost and unusual turbo noises indicate a mechanical problem that could worsen. Continued driving with a failing turbo can lead to more significant engine damage.
  • Diagnostic Scan: Even without a CEL, a professional diagnostic scan might reveal pending codes or historical data related to boost pressure deviations. Look for codes such as:
    • P0299 (Engine Underboost): Indicates the engine is not reaching commanded boost levels.
    • P0234 (Engine Overboost): Less likely with your symptoms, but indicates wastegate control issues.
  • Professional Inspection: It's crucial to have an Audi specialist or dealership service center inspect the turbocharger system. They can perform a boost leak test, visually inspect the turbo and wastegate, and use specialized equipment to diagnose the exact cause of the noise and performance reduction. Addressing this early can prevent a full turbo replacement.
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