I have an 85 300SD in which the door locks which run from a pump in the trunk is not working. Meaning the pump does not turn on when the door key switch is turned. The pump is "000 800 05 48. There are two connectors on the pump. One 2 pin connector is for power and the other I assume is for the door lock controls of either vacuum or pressure.

The one for power I've measure and there is 12 VDC at the connector. The second pin in that connector is brown and goes to ground.


With 12 VDC applied to the pump, shouldn't the pump come on ?

The pump does not come on with the key in the door switch; it comes on when you start the car. The pump builds up pressure which locks and unlocks the doors and should last for some weeks. However I agree that the pump should come alive if you hit it with a 12 volt battery. Or hook it up to your battery charger and see if it works.

I can't speak for the earlier models, but in my '86 W126 I can assure you the pump runs to cycle the locks whether the car is running or not.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Mine is a '81. The pump does not run at all if the engine is not running. Before or after. The vac holds for at least two or three weeks without starting it up again and the locks function.

Thanks Diseasel300. Yes, the vacuum pump is controlled by fuse #13. I've measured this fuse and there is voltage on both sides of the fuse with the ignition off. So I have 12 VDC at the fuse as well as the 2 pin power connector at the pump.


There are three other wires which connect to the second pump connector. They are yellow, brown and green. I assume these pass voltage to the pump from the switch in the door. It appears that these wires control an internal switch within the assembly so the pump is doing vacuum or pressure.



A trouble-shooting method might be to run a ground and hot wire to the pump from a seperate battery. MB's have issues with grounds in my area due to moisture. Then run a seperate jumper to one of the three posts on the second connector. I should here a switch snap and then the pump run. Is this thinking correct ?

Why not just take it out and put it on your battery charger? I did that with mine and it would run. Only problem was that the rubber diaphragm was ruptured and I could not repair or replace it. They are easy to take apart.

My 82 has a pump that will lock out to save itself or the battery if there is a leak in the pneumatic system. The pump knows to stop when the load on the motor changes as after the doors stop unlocking or stop locking. If there’s a leak, the motor would run and run prolly till the battery drains. So somebody designed in a cutoff that gives up after awhile and turns everything off.

As suggested, the way to fix it is get the pump put on the bench and hook two of the three terminals across 12v from a battery or charger. Then it makes this snap sound and starts running again...at least mine does.

I think I have this happen every two years when something goes wrong with the vacuum system. The car came to me this way with non functioning locks. It was quite a shock to resurrect the motor using a 12v supply. Then it was just a matter of finding which lock put it into shutdown.

Edit. Whoa I spoke too soon. Your pump is a tiny bit different than mine. Mine has only a three pin connector. That takes ground, 12v high to open, and the third 12v high to lock. Looks like the 85 has this connector plus a 2pin. Not sure how to test it. I’d take the advice here to tear it down. You’ll be able to see what makes it tick inside. It is still worth checking to see if it is stuck in a fail safe mode.

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

The pump might be different for a car with ortho seats.

Sixto
98 E320s sedan and wagon
02 C320 wagon

Not sure about the ortho seat but any recommendations to taking it apart. I've already moved the back which uncovers the backside of the circuit board. The end without the connector seems to be easy to lift, but the one with the 2 connectors seems to want to come out easily. Do those connector push back thru the assembly and are part the the circuit board or do they usually have wires connected to them ?
Any advise on taking the assembly apart would be quite appreciated. Any suggestions ?

Before taking it to bits, maybe studying your car’s wiring diagram will lead to an understanding of what signals to put into the various connectors. On mine it is three connectors on the circular receptacle with the tab. I just set up my 12v power supply and run different combinations of the two +/- leads to the three wires till I hear it pump. This will often bring it back to life.

Maybe I was a bit hasty saying take it apart. You might be able to figure out what the two pin deal is without ripping into it. Do you have a wiring diagram for your car?

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

The 85 is significantly different than previous models. It uses a solid-state control board and is more than just switched power. In 85, it's also tied into the Central Alarm System.

https://www.startekinfo.com/StarTek/outside/12253/program/ETM/126td83-85.pdf

(The wiring diagrams are 105 pages of pdf so it may take a few tries to get them to download. Once you do, save them on a device.)

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Sam

84 300SD 350K+ miles ( Blue Belle )