izzynumerouno

Hey guys, I have a 03 S500 4MATIC. This was my father’s car before he passed away and i’m currently taking care of it. It has been sitting for a while and I finally got time to change the battery out and start it up. On the first start up there was a loud hissing noise coming from somewhere on the passenger side of the cabin. Every time I start it up now the hissing gets a little quieter but i’m still worried. Any advice would be appreciated, this is my first mercedes and i know there’s a lot i need to learn. Thanks in advanced!

tusabes

Very hard to say what that could be, there are pneumatic powered door locks, and soft close door mechanisms inside the door, which could make it hissing noise. It’s pretty common for the plastic vacuum actuators to break. Check the soft close of the passenger side doors

also their air bladders inside the seat could be those just use your ear, and check these things

izzynumerouno

Thanks for the reply! Just checked, soft close door is good. Hissing is more quiet almost faint coming from either the radio or just to the right.

QUOTE=tusabes;8948705]Very hard to say what that could be, there are pneumatic powered door locks, and soft close door mechanisms inside the door, which could make it hissing noise. It’s pretty common for the plastic vacuum actuators to break. Check the soft close of the passenger side doors

also their air bladders inside the seat could be those just use your ear, and check these things[/QUOTE]

tusabes

There’s some computers in the dash and there’s also a tiny fan in the overhead panel next to the sos button

could also be the AC blend doors inside the dash