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Discussion Starter #1
Hi all, we have had a strange issue for quite some time. I did my research and initially thought the PSE unit must be wet/damp.

Basically the car will lock on the button no problem. But only very rarely will it unlock. There's no activity from the pump at all when you press the unlock button and nothing happens. It never ever fails to lock. It's purely the unlocking which is at fault.

It might not be related, but I'll mention it just in case, but the air bag light came on a while ago and this was said to be a faulty control unit by a specialist. I doubt it has anything to do with the locking issue but as I say, you never know if you don't say anything.

So I took the PSE out of the boot, took the bottom off, left it in a baking hot conservatory for over 48hrs and put it back together, wrapped in a plastic bag to keep it dry.

Absolutely no change. I'm gutted.

I have noticed that the hydraulic fluid is almost right on the minimum line. Could this have anything to do with it? I am picking up some of the correct type of fluid later today. Should I top up or syphon out and refill?

Many thanks for any help/suggestions.
 

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Discussion Starter #3
So I've realised that I'm clutching at straws with the hydraulic fluid as that's just for the roof isn't it?

Moving on!

I didn't look at the solder actually. Wouldn't cracked solder be very difficult to see though? I can take it out again tonight.

Oh and just to eliminate it from suggestions, I did check the fuses.
 

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So I've realised that I'm clutching at straws with the hydraulic fluid as that's just for the roof isn't it?

Moving on!

I didn't look at the solder actually. Wouldn't cracked solder be very difficult to see though? I can take it out again tonight.

Oh and just to eliminate it from suggestions, I did check the fuses.
Right, hydraulic fluid is just for the roof. The locking system is pneumatic.

Well, not looking for cracks but for corrosion. That should be obvious.
 

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Discussion Starter #5
In all honesty, I'm almost certain I took it apart a few months back the first time and couldn't see anything. I will check again but I am 90% sure (this is our second SLK) that I have done this.
 

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Discussion Starter #7
Well here's the really weird thing; if you click unlock on the fob, then unlock the door with the key, no.

If you go to unlock the door without pressing the fob then it will feel as though it is trying to resist you turning the key, but when you do this and then open the door with the handle, the PSE will come to life and unlock everything quite often!
 

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Well here's the really weird thing; if you click unlock on the fob, then unlock the door with the key, no.

If you go to unlock the door without pressing the fob then it will feel as though it is trying to resist you turning the key, but when you do this and then open the door with the handle, the PSE will come to life and unlock everything quite often!
That kind of makes sense to me. The PSE thinks it unlocked the doors with the fob so it does not have to do it again when you unlock at the door.

There is a plug that goes into the door lock that tells the PSE when you are unlocking the car with the key and I wonder if that has been disconnected.
 

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Discussion Starter #9
Where do I find that? I'm happy to check. But ever so occasionally the doors will unlock on the fob so does that rule that out at all?
 

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Where do I find that? I'm happy to check. But ever so occasionally the doors will unlock on the fob so does that rule that out at all?
Under the door panel by the locking/latching mechanism.

I am not sure if it rules it out. But the fact that the key does not unlock all the doors makes me believe there is an issue at the door too.
 

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Discussion Starter #11
Well I found the yellow pump cable in the door, but I didn't find any electrical plugs near the lock mechanism. I've also found that the locking has stopped altogether now...

Apologies for not coming back to update sooner, I didn't have time to get near the car and try anything.
 

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Well I found the yellow pump cable in the door, but I didn't find any electrical plugs near the lock mechanism. I've also found that the locking has stopped altogether now...

Apologies for not coming back to update sooner, I didn't have time to get near the car and try anything.
There should be a plug in the mechanism the yellow hose goes to. Above it somewhere.
 

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Discussion Starter #13
I couldn't see anything like that, certainly nothing hanging loose.

However, the plot has thickened! Last night I decided to go take the PSE unit back out. I don't know how I didn't notice this before, but the cables to the white plug have been taped up! This set alarms bells ringing so I unraveled the tape and found that a few of the wires have been tapped into. WTF?

I'll post a photo shortly, but I suspect this may be the root of my issue.
 
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