Sorry I was sent out of town for school with Mercedes-benz and I forgot my laptop. Sorry for the inconvenience. For some reason I didn't get an email until you relisted the question. The PSE pump for the locks on this model only continues to cycle when a leak is detected in the system. Obviously we don't have the luxury of scanning the pse system with a mercedes computer which will tell you the circuit that is leaking. This greatly narrows down the possibilities. What I found is the easiest way to check is get to the most quiet are you can find and lock the car with the windows rolled up. You will here the pump cycling when your sit in inside the car but listen near each door to see if you can here a small air leak anywhere. Usually the air line can break somewhere behind the door panel or at the door flex point. Sometimes a door lock actuator can leak too but it seems the lines break more often.