My 2011 sl550 doors lock automatically when driving but will not lock with key fob which indicates a vacuum n or Pse issue. Are the systems not related? I don’t understand the difference.

 

When the locks work, they work. You need to concentrate your search on your key fob and the car's signal receiver.

 

The lights flas when I push the button on the fob so I assume the connection is good

 

There are differences in what it is trying to lock. I believe that the auto lock when driving will only lock doors, while the fob may try to lock everything depending on settings. You probably have leaks on the central locking circuit.