We have a 1992 500 SEL and a niggling problem started the other day. On pressing the remote central locking button control the red indicator light on the drivers door (also same problem on passenger door and boot) repeatedly flashes and the central locking does not function. The same is true from the interior locking button. The car operates from a hydraulic system and given the fact that there is no operation (or sign of movement) from the door locks, I assume the issue to be electrical. Any help / guidance would be truly appreciated - i.e. is there a relay? Which fuses function from the system? etc

The symptoms you described, failure of the central locking system were the symtoms I experienced when I had a PSE (Central locking pump) failure. The W140 has two pumps - one in the trunk (door closure assist) and one under the rear seat on the passenger side of the car operates the central locking system, gas pump lid and lumbar support on seats.

It appears you will need to replace is the PSE pump under the rear seat (passpenger side of the car) The item isn't cheap. You can find a new Bosh PSE pump on Ebay for $400ish - dealer wants about $750.

As always, Check the fuses at a 1st step. If the pump is working you will also hear a humming noise coming from under the rear seat location when the system is activated.

PSE pump failure is common in our model of MB.

Russell

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

Really appreciate the reply. It sounds as if you are going to be correct in the diagnosis (much to my dismay of having to spend out a load more money). I took a look at the fuses; however, we are missing the detail on our list and are unable to pinpoint which fuse would control the pump for the central locking system. Are you able to help guide us to the correct fuse number?

Another problem has also arisen; the stereo (standard Becker model fitted with the Bose upgrade speaker package) still appears to fully function, however, with no sound. There is no way to turn the volume up or down as the switch does not appear to function at all. Could this be linked? Any help would be greatly appreciated.

Thanks in advance.

If I remember correctly, the fuse in question, the one that protects the PSE (Central locking system) is fuse #3 located in the fuse pannel in the trunk.

Since you are unable to see the detail in your fuse pannel description, I have attached the info.

Attached Thumbnails

 

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

Bernard,

I doubt there is a relationship between the problems you are having with the car's Bose/Amp Radio and PSE failure. Both items are notorious for failing in the early model S-Class MB. The BOSE 7 channel amp is guaranteed to fail - it's just a matter of time. The amps were manufactured with diodes that erode over time. The normal path of failure for the BOSE amps is cracking and hissing that you hear coming from the speakers that gets worse over time. I'm no electronics person, but I guess a sudden failure is possible for the amp. Maybe someone else can comment regarding this matter.

If the radio problem happened suddenly, especially if you've been rummaging around the trunk looking for fuses for your PSE pump failure, I would check the connecting cables to the rear radio tuner. The Becker radio you have is divided into 3 components. The head unit (this is what you are calling the radio in the dash), the tuner is located in the trunk next to the antenna, and the BOSE 7 channel amp. The amp is also located next to the rear Becker radio tuner in the trunk. The tuner has a fuse on the back next to where the cables connect. Check the tuner's fuse and all connecting cables.

Just a side note, if you decide to replace your own PSE pump located under your rear seat, you will need to get an adapter kit since you have the earlier model of PSE pump. Search on my id to see pictures of the new and old model PSE pump.

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

Russel,
You are completey correct except it is electrolitic capacitors that fail, and they are in the tuner also, it is rare that the entire amp fails in one whack, the fuse in the tuner could blow, and yes if it had a CD the cables could be loose. The control head usually indicates faults ( but not bad "bose amps")
The pse also controls the lumbars, trunk lid handle, vacuum at rest for the HVAC and the back up rods, if those dont work it could help trouble shooting.
If the system senses a leak it also shuts down, but after resetting you should hear ir 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, whereas the remotes interface to the pump also