The pnuematic system pump (PSE computer) has different "jobs" which including door locks, back-up assist (depending on your model), headrest fold-down (rear seat), ortho-seats, retractable trunk handle. This is the pump that is located under the passenger rear seat.

The PSE pump DOES not control door closure assist. Door closure assist is controlled by a separate pump located in the trunk next to radio amp on the driver’s side.

As always, check the fuses at a 1st step. (in the trunk fuse panel) I cant remember if this is fuse # 9 or # 3 .. check your diagram) By removing the fuse and reinserting the fuse, after waiting a few seconds you can reset the pump sometimes providing a temporary fix to your PSE pump problem. (kind of like reboot a computer) If the pump is working you will also hear a humming noise coming from under the rear seat location when the system is activated.

As a side note: If the system senses a leak it also shuts down, but after resetting you should hear it run. There is a 10 second shut down in locking and a 60 sec shut down in consumers. I would try the keys since they control the pump directly.

PSE pump failure is common in our model of MB. I think the dealer part cost is about $750. If you’re mechanically inclined you can find a replacement pump and install it yourself. Phil at Fastlane can give you a better price. FYI.. MB has moved to “universal PSE” pump, so you may need additional hose connectors to complete your replacement.

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Russell McMahon
Tulsa, OK
2001 CLK 320
1992 400se
1993 400e
2000 320ML