'91 500 SL Vacuum Pump
 

Following engine start-up or with just ignition on the vacuum pump runs for 1 sec followed by an 8 sec off interval. The pump continuously repeats this cycle until denergized.

With the ignition off, the pump only runs briefly (less than a second) in response to a central locking system command to either open or close the lock elements and then stops.

The central locking system is functional - door and trunk vacuum elements operate properly and with no lag time.

Is the cycling of the pump indicative of a vacuum leak or is there a problem with the pump activation circuit?