W126 Door lock vac pump reset issue - PeachParts Mercedes-Benz Forum

bgkast · #1 02-27-2009, 08:56 PM

Once every month or so I will go to lock the doors in my SD and they will not all lock. I can solve the problem by disconnecting the battery for a second to reset the vac pump, but I would like to know why it is happening. I do not have any leaks in my door lock system and the locks function normally and quickly when they do work. Any idea what could cause this?

81300sd · #2 02-27-2009, 08:59 PM

Just guessing but maybe your pump is weak

tyl604 · #3 02-27-2009, 11:21 PM

I do not know anything that could get reset in the pump. I think you just have a pump problem. It is probably in the trunk by the spare; check it out. But do not take it apart and look - that is what I did and I ruined a perfectly good pump. Cost me a cool $100 to replace. '81 300sd

bgkast · #4 02-28-2009, 01:25 AM

How long does it take your pumps to unlock/lock the doors? It takes mine about 2 seconds.

Dee8go · #5 02-28-2009, 09:19 AM

Quote:

Originally Posted by tyl604

I do not know anything that could get reset in the pump. I think you just have a pump problem. It is probably in the trunk by the spare; check it out. But do not take it apart and look - that is what I did and I ruined a perfectly good pump. Cost me a cool $100 to replace. '81 300sd

How would you test the pump to find out if that's where the problem was?

tyl604 · #6 02-28-2009, 09:39 AM

The only thing I can think of is to remove it, connect it to a DC current (I use my battery charger), apply current and see if you have vacuum. Of course you should test it first with the Mityvac to make sure it does not leak vacuum. When I put mine back together, it would never hold vacuum although it pumped like crazy.

81300sd · #7 02-28-2009, 11:34 AM

Mine takes 2-3 seconds to lock or unlock but the pump runs for about 5-6 seconds. Seems longer than it used to be but then I only use my remote now so that may skew the results.

#8 02-28-2009, 12:16 PM

I had the same issue with my 83 300SD and ended up replacing the pump. I have a spare car luckily!! It does sort of reset but you don't have to pull the batt cable to do so, just unplug the unit located in the trunk and it "re-sets" that way. Must be some sort of time out device that after it runs for a while it stops working till re-set....at least it worked that way with mine.

cdplayer · #9 02-28-2009, 12:39 PM

W126 and W201 cars from 1981 to 1984 used a simple 3 wire electrical vac pump. There are three different outer case designs, but they all do the same and can be interchanged. The electrical plug on all three is the same. These are the ones I look for all the time when I am out collecting parts to sell. Cars 1985 and later have a second electrical connection. I haven't figured out how to test these yet.
I also use a battery charger to give me the 12V power to test the pumps I get. There is a blue,brown,and yellow wire. Always connect your negative battery charger cable to the brown. Connect the positive to one of the other wires. Does not matter. Depending on the pumps cycle when it was used last, it should run producing a suction or producing a pushing action. You can feel the vacuum port to tell. If the pump does not start, then hook the positive cable to the other color(blue or yellow) wire. If the pump is good it will fire up.
Now, while the pump is running(it will continue without stopping) plug the vacuum port with your finger. If the pressure regulator is good, it will cut power to the pump. It successful, hook the positive cable to the other color wire(blue or yellow) and retest plugging the vacuum port with your finger. The pump should stop instantly if working properly.
If you guys need this pump, I keep a dozen on hand all the time. Each tested and work perfectly. $60.99 shipped USPS Priority mail to your US address with delivery confirmation.
I am not a business. Just retired and using my hobby to help make ends meet. If interested, PM me for PayPal information. Or if you have any questions. Thanks. Dan(cdplayer)

Quote:

Originally Posted by Dee8go

How would you test the pump to find out if that's where the problem was?

bluebird · #10 02-28-2009, 01:52 PM

BG, I had a similar situation on mine last winter. I figured out that if I unlocked the passenger door to avoid unlocking all the doors and then pushed the button down to lock that door then the pump got confussed and I could not unlock the trunk. If I locked that door with the key the problem disappeared. I also noticed a cable wire going along the back driver side to under the back seat. I havn't pull tested it yet as my problem no longer exists.

When the problem did exist all I had to do to REPAIR it was to lock and unlock the passenger door with the key and the car was back to normal.

Best of luck with your problem.

81300sd · #11 02-28-2009, 01:57 PM

The 81 if only controlled by the drivers door is a different pump and not compatable with the later pumps or so my fsm says. I do know that the wiring is different as my 81 is.

bgkast · #12 02-28-2009, 02:19 PM

My pump seems to be working fine. When I got the car it had a bad passenger door actuator and the pump would run for 10 seconds or so, then time out and would need to be reset by unplugging the battery. Now that I have fixed the vacuum system it only runs for 2 seconds then stops when all the doors are locked/unlocked.

I do recall using the passenger lock around the same time that the problem occurred this last time, but I'm not sure if it was before or after the problem... I'll try to pay attention and see if the next time it happens I have used the passenger lock recently.