W220 Central Locking not working

[MBAdam]

Hi, my 2002 S 320 CDI central locking has stopped working. The lights flash and the alarm sets but the doors won't lock. The lock and unlock buttons don't work on the dahsboard either. Also the rear headrests won't fold back from the switch on the dashboard either. Can't find the fuse desigantion diagram in the boot! However, found a 20A fuse in the box under the rear seat which keeps blowing. Any ideas??

 

[Voltman]

Had same problem a while back on my last W220 S320 (2000). Only happened when there was a frost. Took it to dealers and they said there was moisture in the airlines that work the central locking and that the moisture was freezing so stopping the system from working. The fuse would blow to stop damage to the pump. They quoted mega money to try to fix it so i put up with it. The only way to get round this was to open the drivers door with the mechanical key.Also switch of the automatic locking system as this will blow the fuse when you set off. The fuse is located under the seat and is a yellow 20amp if i remember rightly.

 

[MBAdam]

More detais

Hi, Thanks for the responce. Had a better look at it today. One of the 20A fuses under the rear seat keeps blowing, but I can hear a ticking noise from the rear right hand side of the boot where there is a foam covered box and I am getting a warning saying pre safe is inactive. Ticking stops when fuse blows. Any ideas. Phoned the local MB dealer who wanted to charge me £180 to come out and look at it because the MB independant I bought it from did the last service which invalidated their breakdown support - go figure!

 

[Voltman]

The noise is coming from the pump which is located at the back of the boot. The fuse blows to protect the pump. Does the fuse only blow when there's a frost, if it does then it could be same problem i had. I think you need to get the air lines checked first to make sure theres no leak or if there's moisture in them. Hope this helps.

 

[Dieselman]

I think you have either a vacuum leak or the comfort pump is u/s. I'd go for the pump as the fuse blows.

 

[zerocool]

yeah pump is a favourite on 230 models too,blows the fuse and renders the central locking inop,cause is water ingress into the pump or the connector on the pump,you could try checked the electrical connections for water damage first etc

 

[MBAdam]

High guys, got it fixed in the end. As you said it was the pump that was broken. The part cost nearly £400 before VAT, ohch!