Pneumatic Doors 1992 400SE

Recently, I purchased a 1992 400SE. Upon reading the owners manual, I became aware that there is a pneumatic door assist in the normal closing of the doors and trunk lid. This system is not functioning at the present time. ( None of the doors or the trunk lid pneumatically close, they must be "slammed" closed. ) Is there something simple that can be checked by me before taking it in for service?

Thanks in advance....

Dan