1993 500SL Central Locking Pump / Locking issue

[MJM]

Hello everyone,

I just purchased this car and was told the central locking pump was dead which caused the doors to not lock unlock. Really I had no reason to doubt the fact the pump was dead and this didn't scare me since replacing the pump is pretty straight forward.

Tonight I started to tear into the trunk and found that in fact the pump does run. Here is the problem...

The remote will trigger the Red/Green light on the door and make the pump run however none of the doors or compartments inside the car open. If I put my key into the door and lock/unlock the pump runs but the action of the key is only locking the drivers door. (One funny thing is the red/green light blinks when I use the key to operate the door and keeps blinking for some time)

Right now all of the compartments inside the car are locked and I have yet to get them to unlock. I checked all of the connections on the pneumatic pump and all of them are snapped in and snug. From what I can see none of the tubes are bent or folded over.

As a side note if I lock the car with the remote (red light blinks) and wait 30 seconds to open a door the alarm doesn't sound.

I really, really thank anyone who has some insight or direction. So much for a quick fix.

Thank you again.

Matthew

[wjsal]

Had a similar problem.... although the pump was making noise, it wasn't creating the vacuum needed to operate the locks. I replaced the pump and everything is fine.....

[MJM]

Hello,

That would be way too easy. I guess I should make sure I've got a working pump first before checking lines for a leaks.

Any way to see if the pump is actually creating a vacuum?

Matthew

[bobterry99]

Borrow a hand-held vacuum pump from Autozone. It has a gauge so you can apply a vacuum to a line and then see if it leaks.

[MJM]

Hello,

That is an excellent suggestion. Can I damage anything by applying vacuum to the wrong lines? I'm not sure which lines are which on that pump.

Thank you.

Matthew

[stevecora46]

My trunk lock would not operate when I first got my 92 300SL. All of the other locks worked OK, but the pump would run for quite a while (30-45 seconds), then shut off. I found a leak in one of the plastic tubes, which created a weak vacuum on the whole system. I used a Bic ink pen filler to splice the hose and everything works perfect.

[Dec McDermott]

Hi Matthew,
Can you tell me if you managed to sort your problem as I seem to be suffering similiar symptoms.
Thanks,
Dec.

[LeaUK]

The red lamps flash to indicate one (or all) of the locks are not locked, hence indicating a locking failure.

Sounds to me like not enough vacuum for several reasons.

Lea