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S-Class (W221) 2007-2013: S 320 CDI, S 350, S 450, S 500, S 550, S 420 CDI, S 600

New to me W221, does it hiss once engine is off?

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Old Sep 8, 2025 | 10:35 PM
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Porsche 911
New to me W221, does it hiss once engine is off?
When I power off the car, it sounds like the air suspension hisses then stops. Is this normal?
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Old Sep 9, 2025 | 08:22 AM
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2013 S550 4MATIC
Yes.
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Old Sep 9, 2025 | 08:26 AM
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1983 Nissan Shltbox
Yup. Like a snake. I believe there's a filter near the compressor that can contribute to this. Relatively easy to replace, but I like the hissing so I leave mine (:
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Old Sep 9, 2025 | 08:54 AM
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Yes, that's completely normal. It's just the system venting air pressure when you shut it down. You'll usually hear it from the valves under the vehicle. Nothing to worry about.
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Old Sep 10, 2025 | 07:27 AM
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clk320
Under the right front wheel fender liner is an air regulator with air lines running into it. One of the lines is cracked or disconnected. If you repair the broken line, the noise will decrease significantly or stop completely.
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Old Sep 10, 2025 | 07:31 AM
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From: Fleriduh
W212 E63S Wagon - GSL580 - E63 - E350 - C300
Originally Posted by mcb66
the noise will decrease significantly or stop completely.
Since when? My car(s)...three of them all hiss, vent and pump randomly just to mess with my head in the garage (and attract snakes).
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Old Sep 10, 2025 | 07:44 AM
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clk320
..
Last edited by mcb66; Sep 10, 2025 at 07:47 AM.
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Old Sep 10, 2025 | 07:45 AM
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clk320
Originally Posted by OldManAndHisCar
Since when? My car(s)...three of them all hiss, vent and pump randomly just to mess with my head in the garage (and attract snakes).
Have you repaired the hose(s)?
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Old Sep 10, 2025 | 08:09 AM
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From: Fleriduh
W212 E63S Wagon - GSL580 - E63 - E350 - C300
Originally Posted by mcb66
Have you repaired the hose(s)?

This has been a normal thing...since the cars were purchased brand new from the dealership. It is simply part of the air suspension system...thus, so many comments that it is normal.
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Old Sep 10, 2025 | 11:42 AM
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2013 S550 4MATIC
Originally Posted by mcb66
Under the right front wheel fender liner is an air regulator with air lines running into it. One of the lines is cracked or disconnected. If you repair the broken line, the noise will decrease significantly or stop completely.
No such thing of " stop hissing " The air system collects air as well as it releases it. Therefore there is always going to be air being released from the car.
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Old Sep 10, 2025 | 11:09 PM
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2010 MB S550, 2017 MB SLC 300
100% normal.
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Old Sep 11, 2025 | 02:38 AM
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W212 FL
I have seen various models including the present W214 E Class, it does also make a similar sound . I think it's the way how the compressor works .
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