Mercedes SL400 Rattle From Wastegate Valve
If you’ve got a Mercedes or AMG model with a turbocharged M276DELA engine and you’ve started to notice a rattling noise when lightly accelerating or cruising along — don’t panic. You’re not the only one hearing it, and thankfully, it’s not a major issue but years later it can be. Let’s break down what’s causing the sound and what (if anything) needs to be done about it. Mercedes wastegate valve rattle issues can lead, however over the years to wastegate shaft bush wear and develops radial play of the shaft due to mentioned Mercedes fix bellow we believe due to excessive force applied by wastegate valve actuator as we had Mercedes SL400 5 years old with this strange wastegate bush wear and rattle on cold start we believe is linked and potentially a cause of the Mercedes offered fix bellow.
What’s That Rattling Sound?
The noise usually shows up during partial throttle — meaning light acceleration or when you’re just maintaining speed. It’s a bit of a metallic rattle that sounds like something loose under the bonnet. And while it might sound alarming, it’s actually coming from the turbocharger’s wastegate — a small valve that controls turbo pressure. This issue is reported on static.nhtsa and Mercedes bulletin.
🎧 Mercedes even has an example of what it sounds like: “M276DELA Wastegate.mp3” — just in case you want to compare.
So, What’s Causing It?
Here’s the deal:
- On regular Mercedes-Benz models, the wastegate’s valve disc can vibrate slightly when it’s partially open. That’s what creates the rattle.
- On AMG versions, the noise comes from the wastegate disc tapping against the actuator arm when it’s open.
Basically, it’s just a side effect of the way the turbo system works — not a broken part or anything dangerous however it shouldn’t make a noise but Mercedes want’s to make it sound like it’s not a big issue clearly the valve disc has too much of the play.
Is There a Fix?
✅ If You Have a Regular Mercedes (Not AMG)
Yes, there’s a simple software tweak that your mechanic or dealer can do with Mercedes’ diagnostic system (called Xentry). Here’s how it works:
- The engine control unit gets updated to keep the wastegate closed longer during light driving.
- This stops the rattle from happening during those half-throttle moments.
- The update involves adding a small setting change (called AO code 31O).
💬 Heads-up: After the update, you might notice a bit of a turbo hiss instead of the rattle — also totally normal.
🚫 One exception: If you’ve got an SL-Class (model 231), don’t bother — this setting already comes adjusted from the factory.
❌ If You’ve Got an AMG (Entry-Level Performance Model)
Unfortunately, there’s no fix available. The noise is just part of how the turbo behaves in those cars — it doesn’t mean anything’s wrong. It’s more of a quirk than a problem.
Quick Recap
| Your Car | Fix? | Notes |
|---|---|---|
| Mercedes with M276DELA | ✅ Yes | Software update via Xentry |
| AMG with M276DELA | ❌ No | Normal behavior, no update |
| SL-Class (Model 231) | ❌ No | Already adjusted from factory |
Final Thoughts
That annoying rattle under light acceleration in your Mercedes isn’t a major fault — it’s just a part of how the wastegate operates that is Mercedes explanation but it does,t operate this way as 99.9% don’t have this problem unless the fault develops or it’s inherent fault as it looks more likely from Mercedes design issue. If it really bothers you and you’ve got a standard Mercedes model (not an AMG), a quick trip to a garage with Mercedes software tools can sort it out however that bulletin was 2021 year.