WIS 88.50 Trunk/Boot Lid
Hissing Sound on Trunk Closure
- Issue
This issue applies to vehicles with auto closing trunk and later ones post facelift 2003 which if they don't have the auto close feature have the Retractable Trunk Lid Grip (RTG) or retracting chrome handle feature.
After the boot lid is closed there is a hissing noise as the lid is pulled down tight and then the chrome handle retracts. General opinion is that the M-B design purpose for a hidden handle was to avoid the operator having to touch a wet handle in inclement conditions. STAR DAS refers to it as the "dirt free handle".
- Hissing Noise Cause
A persistent loud hissing noise once you close your trunk is not normal and usually means that you have a tiny leak and may need a new trunk lock actuator or a small crack in the yellow vacuum hose to the locking mechanism.
It will eventually stop leaking once the leak gets worse. Hopefully the pump will recognise that it is running for too long and will stop working so that it doesn't burn out. Then the trunk stops sucking down. Do not leave in this condition for too long because when the trunk stops sucking down water can get in and ruin your electronic components in the left side of the trunk behind the panels. There is also a possibility of damaging the pump due to constant running.
- Repair Vacuum Hose Solution
The hissing is often caused by a crack in the yellow vacuum hose that is located inside the black braided plastic harness which is easily visible on the inside of the trunk towards the rear window. You can see it when the trunk opens and closes. For whatever reason M-B used a very stiff pipe which cracks easily.
A common mistake is that when you have some aftermarket installation such as a reversing camera, the installer runs their wires alongside the harness, and adheres their wires to this with the additional strain causing premature failure of the vacuum hose.
A simple fix is to use a rubber hose to cover the crack and seal it with adhesive, sealer, tape and plastic ties.
Reference: http://www.benzworld.org/forums/showthread.php?t=1761754