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MB Paul
MB Paul, Mercedes Technician
Category: Mercedes
Satisfied Customers: 4317
Experience:  Mercedes Benz Qualified Diagnostic Technician
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The boot on my SL350 would not open last night. I was able

Customer Question

The boot on my SL350 would not open last night.

I was able to open it with the key this morning but the doors and boot wont lock using the central locking now.

Any ideas?
Submitted: 3 years ago.
Category: Mercedes
Expert:  MB Paul replied 3 years ago.

MB Paul :

Hi, I would always recommend a full diagnostic check on Mercedes STAR diagnostic tool to help pinpoint the problem but on the SL model the most common issue is the PSE pump which controls the central locking which is located in the left of the boot. This can fail on its own or also commonly due to moisture or water ingress through poor roof seals - especially the lower rear screen seal.

MB Paul :

In the first instance you should check fuse no 71 in the rear fuse box (located under the rear storage compartment behind the drivers seat) - if blown you can try replacing this - sometimes the system will work again for a short while or may even just be a one off blow - if it blows again then the PSE pump will certainly need replacing.

MB Paul :

The pump can also fail without blowing the fuse so it is not a sure fire test but simply the first step - if this is ok then the car will need checking on STAR to see if communication is possible with the PSE control unit

MB Paul :

There are of course other possibilities but this is the most common on the SL

MB Paul :

Best regards, Paul

JACUSTOMER-biem33py- :

can I buy a replacement pump without going to mercedes garage.

JACUSTOMER-biem33py- :

Any idea what the PSE pump costs and how much labour involved in replacing it?

MB Paul :

Hi - from memory a new pump from Mercedes is around £800, it will also need coding on STAR after installation. Actually replacing it is not too bad - you need to remove the boot floor covering, unscrew the roof pump on the left of the trunk and lift it out of the way & the PSE pump is located under here

MB Paul :

Another cheaper option if your unit is faulty is a specialist company have yours repaired

MB Paul :

Here is a company I have used before: BBA Reman

MB Paul :

It also has the added benefit of not needing coding after installation if they repair yours

MB Paul :

Best regards, Paul

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