1999 SL500 R129 Doors Not Locking with FOB Issue

[blackharp]

Hello all. My sincerest for your help in advance.

I have a 1999 SL500, in Desert Sand (beautiful condition), and a couple months ago, the central locking started giving me problems. At first it was locking everything inside without me pressing any buttons. My girlfriend had to climb over the center console to escape. Very dangerous. Then, I would press the key fob to lock the doors and the lights would blink as it registered, but the doors would remain unlocked, so I have to lock manually. Now, the trunk randomly opens and is open sometimes if I go outside and take a look, the alarm goes off randomly, and it unlocks itself if it feels like it. I am still unable to lock or unlock the doors with the fob even though the lights blink.

I have replaced the battery without resolution. I also pulled out the vacuum pump to examine it because I have read I may need to replace it. I did not pull out and open it up because when I unlock the trunk, I can hear it. I tried unplugging a black tube and noticed there is air pumping out, so the pump itself seems ok. All the tubes are in like new condition, so I can't see a leak anywhere and am not sure where to go from here.

Please help!

Thank you

 

[Blobcat]

Hello and welcome

Sounds like a water ingress issue that’s playing havoc with the electrics

 

[blackharp]

Thanks, Blobcat.

The seals are in excellent shape and I do not see any signs of water at all.

Where might I start looking with your idea in mind?

 

[Blobcat]

@Wearsafoxhat and @LostKiwi both have R129 500’s so should be able to give some advice

 

[Wearsafoxhat]

Good morning,
seems that you have checked most of the likely bits, but
it does seem to sound like a water ingress problem. The fuel line / hose and drain from the filler cap run above the some of the electrics below the vacuum unit and are known to perish.


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[blackharp]

Thanks for the reply, @Wearsafoxhat

What is known to perish exactly? The fuel line and drain, or some of the electrics? Any more info on what these electrics are or what to test to resolve my issue?

Thanks again.

 

[Wearsafoxhat]

The filler hose, the piece of tube connected to the filler cap leading away to the tank can be the culprit. Being petrol it will soon evaporate leaving less clues..


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[blackharp]

@Wearsafoxhat - What I am gathering is that one possibility would be that the fuel line has been leaking onto the "electrics" at the bottom of the vacuum pump. Do you have any more information on the electrics you mention? Any more info on how to fix my issue? Any more info would really help a lot.

I checked this morning and did not see any obvious signs of fuel leakage. Are there any other possibilities that I could check for?

 

[LostKiwi]

The filler neck seal can also perish and leak water into the boot straight on top of the central locking pump

 

[blackharp]

@LostKiwi - Thank you. What is the fix in this case? Is there an "electrics" part number you could reference? Do I replace the entire vacuum assembly? As stated above, there is significant air pressure coming from the pump, so I'm not sure how it would be failing.

 

[LostKiwi]

Remove the pump, disassemble it and inspect the circuit board. Any signs of water ingress and there's your issue.

 

[blackharp]

Remove the pump, disassemble it and inspect the circuit board. Any signs of water ingress and there's your issue.

Thank you, I'll try that.

 

[blackharp]

Does anyone have another suggestion? There does not seem to be any signs of "water ingress."

 

[LostKiwi]

Have you any access to Star?

 

[blackharp]

Have you any access to Star?

I wish I knew what that was!

 

[Timeandleisure]

Since you may be looking for out of the box clues, I had a similar issue, albeit not so severe with my R230. The dealership told me it was the siren (alarm), I let them change it (only they know if they did), no troubles since....

 

[LostKiwi]

That'll be a no then...

Star is the diagnostic system for analysing faults on Mercedes. Sometimes also referred to as DAS or Xentry. Putting it on Star may give some pointers as to where the problem lies.

 

[blackharp]

That'll be a no then...

Star is the diagnostic system for analysing faults on Mercedes. Sometimes also referred to as DAS or Xentry. Putting it on Star may give some pointers as to where the problem lies.

Ah. I only have a generic ODB reader.

 

[blackharp]

Since you may be looking for out of the box clues, I had a similar issue, albeit not so severe with my R230. The dealership told me it was the siren (alarm), I let them change it (only they know if they did), no troubles since....

Interesting!

 

[LostKiwi]

Ah. I only have a generic ODB reader.

So that won't be able to interrogate the central locking components.