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1991 MB 500SL + 2015 MB E250
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Discussion Starter · #1 ·
I would be very thankful if one of you could give me a hint of what's wrong befoe I have to buy a new vacum/compressor unt. The pump does not operate at all when I use the remote or turn the key in any lock. When I push the key-knob or turn the key, the read light flashes for about 10 sec and when I press it again the green light flashes about 3 sec. But non of the locks operate and my orthopedic seats does not adjust any more. I'm quite sure it must be lag of air pressure/vacuum and therefore the pump above the battery. There is no sound when i use the remote or lock any of the locks manually with the key.
Is there no relay? The fuses in both the the trunk and in the engine compartment are all OK including no 6 in the trunk and there is +12volts at both ends of all the fuses (incl no 6) in the trunk at all times.
It is strange that suddenly the pump stops working - I don't recall I have touched it and all connections (pneumatic as well as electrical) connections to the pump and (what I assume must be) the control box (fastened by one Phillips-screw beside the pump) looks undamaged/untouched and in place.
 

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97 SL500
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1,259 Posts
maybe you can run a wire directly from the batt to the pump (just to test) make sure you put an inline fuse to protect the batt. if it works you know there is a bad fuse somewhere or a broken line somewhere.
 

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one of the vacuum lines inside the pump might have worked itself loose. it happened to me and to another member of this forum too. just dismantle the pump and have a look. i am not mechanically minded and i hate to work myself on my cars i'd rather pay someone to do it. but i still gave it a shot and the problem was fixed. i saved about 280 uk sterling pounds, which is over 500 american dollars. search about it in this forum i think i've posted my story on here before.
 

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1991 MB 500SL + 2015 MB E250
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23 Posts
Discussion Starter · #5 ·
Thanks a lot both carlos and Banana.
I have had an extra look at the pump and took of the electrical wire. There is +12v on 8 out of the 12 pins and mass on the other 4. I'm a little nervous to follow the good idea from Carlos as I may damage the pump (if it's not already damaged) if I connect + to a wrong pin. If I just knew how it works and what pins should make it operate. Maybe even it need mass on a pin to start?? Who knows?
If no one has a wire diagramme and would know how to test it, I will follow the suggestion of Banana and hope to be able to refit all the 9 vacuum/pressure lines in their right places again.
I have takne the pump out of the cover, but how do I take the pump apart? There seams to be no screws. Should I just use a screwdriver and use force at the bottom?
I have looked at Bananas earlier advise and experinces. But my pump do not even make a sound. Maybe the electrical motor inside is damaged. I will find out if I dare to force it open.
 

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Outstanding Contributor
2005 SL600, 2003 SL55, 1990 300SL
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Jacob, power from the battery should come to the pump on socket #2 of its connector, and ground should be socket #12.

In an email reply to you I mentioned reading codes for the locking system. You can also do the following test. Remove the connector to the remote control module and shove a wire into socket #23. This is the control signal from the remote module to the pump. Touch the other end of the wire to chassis ground: the pump should run to lock the car; touch the wire to battery voltage and the pump should run to unlock the car. If it doesn't, then I would disassemble the pump -- a procedure for which I have no instructions.
 

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I would do what bobterry advised you first because bobterry is the SL GOD. if that doesnt work then dissassemble the pump. and yes if i remember right there are no screws so with a screw driver or a knife i think you just have to force it open.

p.s: my pump was still pumping it just was not locking anything. i think your pump is totally dead so it cannot be a vacuum problem. i'm not sure, good luck anyway.
 

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1991 MB 500SL + 2015 MB E250
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Discussion Starter · #8 ·
Thanks a lot Bob and others. Thast's an easy test. Unfortunately, nothing happens: No sound - not even a small spark. I'm sure I did the right thing. The box I took of is 129 820 06 26 and connected the #23 of the wire I took out of the box to mass and thereafter tried + on the car battery.
I will now conclude that the box most likely is OK but the error must be in the pump. In the weekend I will try to take it apart and have a look, but be prepared to buy a new. Thank you again for spending your time on my problem.
I hope one day to be able to give others some tips.
Already now I want further spead the "news" that leaking hydraulick cylinders are no problem: Easy to take out and refit and Dennis Ficken repairs them fast and excellent at a very low price.
 

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1991 MB 500SL + 2015 MB E250
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Discussion Starter · #9 ·
I have disassembled the pump. It is very easy: first remove the two blocks where the lines go in and then two Phillips crews can be removed. The bottom can then be gently removed using a pair of flat screwdrivers.
I showed + and - directly to the motor and it work just fine both ways creating both vacuum and pressure. I have then tried all combinations of + and - to all the pins and I can't get the motor to run through this way and only one of the relays to “click”. Now:
1: Is there any chance that if I now educate myself and read and reset the codes, it will come to live again?
2: Can it possibly be the box (129 820 06 26) that causes the problem
3: Is there any guarantee that if I buy a new pump, it will not be damaged by same error that caused the problem in the first place?
 

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2005 SL600, 2003 SL55, 1990 300SL
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Jacob500SL said:
1: Is there any chance that if I now educate myself and read and reset the codes, it will come to live again?
I don't think so.

Jacob500SL said:
2: Can it possibly be the box (129 820 06 26) that causes the problem
No, as this is only the locking/unlocking signal from the infrared remote control.

Jacob500SL said:
3: Is there any guarantee that if I buy a new pump, it will not be damaged by same error that caused the problem in the first place?
There is no guarantee, but I don't think you have to worry about this.
 
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