I'm having a strange issue with my door locks in my 1991 300TE.
When locking with the key or from inside, they all seem to lock fine (one after the other). Pushing the driver's side door lock down engages the others (including tailgate and fuel door) in sequence.

The problem is that 9 times out of 10 (maybe only 8) in about 30 seconds they pop back up. Now this is not a real tragedy, as I rarely lock my car, however the times I DO want to lock it (leaving it in the city or airport for extended periods of time...) This is a little annoying.

It even happens while driving! The problem is that when I open the doors again they security system turns on and the headlights flash until I lock the car from the drvr door and unlock again with key. Do you have any suggestions?

Thanks!

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Current: '91 300TE 4MATIC 317k and climbing...
Former:
'81 300TD Wagon 168K "Tank"
'83 240D 216K 4spd manual "Da Bear" (aka best car ever)

"Never sweat the petty things...
and never pet the sweaty things."

you have a bit of a wiring problem in the driver door lock that activates the pump.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

I suspect it is a faulty vacuum pump which controls the central locking. You can do this to narrow down the problem.

1) Does the same happen when you try to lock/unlock from the pass door using key or push/pull the plunger?
2) Does the same happen when you try to lock/unlock from the trunk?

If it happens with (1) and (2) then it is probably the pump. It it does not then it may be the driver's vacuum pod wiring not latching.

Good luck.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.