What part is this
 

What is this and should there be a hose attached to going somewhere?

Hi Steven,

If other members in the forum do not chime in to help with the part ID, feel free to give us a call at 888-280-7799 or shoot us an email and one of our MB part specialists will be happy to help you out. Hope this helps and best of luck!

Thank you! I'm guessing that's why my door locks don't go up or down. Should I look for leaks in the lock system, fix it and hook the check valve back up, or just live without it? How do I get the door locks to work without it? I'd kinda like to lock the car if I take it anywhere.