rsmcmahon

I have a 92 400SE W140 that yesterday the Central Locking System stopped working. I first checked the fuses in the rear of the car and discovered the fuse (F4 # 9 20amp) had blown. What is interesting F4 # 9 specifically controls the “closing assist” function while F4 #3 fuse controls central locking, closing assist, and the PSE control module. I replaced the blow fuse and the central locking system worked for a few minutes before the fuse burned out again. I could hear the PSE pump under the rear seat running when I attempted to activate the central locking system. I replaced the blow fuse again (F4 # 9) but now the PSE pump does not run. I you attempt to use the Central Locking System, you will only hear a single, faint click noise coming from the PSE pump – no motor running. The door and trunk Closing Assist work fine, but none of the PSE controlled modules work.

Since the PSE only makes a faint, single click noise, is the PSE blown and needs to be replaced? Does anyone know why the fuse was blown on F4#3 for closing assist when the PSE pump (PSE is controlled by F4 #9) is not controlled by this fuse?

I also checked the vacuum lines that connect to the PSE pump and all connecting lines with the exception of 3 will hold a vacuum without loosing pressure. Do you think these 3 lines caused the PSE pump to fail due to overwork?

Peter Guenther

I have posted on this subject many times on various forums, here goes. The pump supports a lot of activity, vacum/pressue for lock unlock (it runs both ways) which applies to back up rods, the retractable trunk handle. It provides vacum for the HVAC, and for the headrests (if you dont have the electric rear seat). It provides pressure for the lumbar system.
It will time out in 10 seconds if there is la leak in the locking system, and in 60 seconds if there is a leak in any of the other systems, except the ortho which will continue to provide 600 mbar if it looses pressure. You have to understand that once a lock or unlock is reached the system no longer needs to provide pressure or vacum.
I wish you would have identified which line would not hold vacum/pressure.
1. yellow-locking
2. orange-backup
3. black-trunk lid grip
4. gray- orthopedic
5. transparent -HVAC
Why did the fuses blow, I have no idea unless there is some sharing of power! The click could be the relay for the pump, but the pump could be fried, locked up or otherwise causing the fuse to blow

rsmcmahon

Peter Guenther,

"I wish you would have identified which line would not hold vacum/pressure"

Thanks for the help and information. If you will notice in the attached pic of the PSE lines there are two gray lines and 1 black line that will not hold a vacume.

Thanks again.

Russell