R129, what does this do?

[truck71]

Hi Folks, trying to get the remote central locking going on my R129 and the issue appears to be with the key fob (the spare flat credit card type key works fine). I've replaced the batteries in the fob but to no avail so question- what does the red thing do pictured with the fob below? It looks like it might plug into something?

[truck71]

MarsellusWallace said:

It's a Mercedes security alarm/immobiliser system master key,factory fit.

Ah thanks, sounds encouraging. Any idea how it should be used? I've noticed a potential female receive point on the drivers side door frame. Unfortunately the handbook doesn't make reference to either the fob or its use.

[truck71]

Thanks, your last sentence gives me hope I can source/ match a new fob. Subject to Merc tax of course.

[truck71]

GXMAMG said:

The red key looks very similar to the master "key" on the impbilser on my mk3 golf. That came with no black keys and it left me stranded in a car-park because you can only use the master key to "start" the car a few times before it says it won't play ball.

I found some on ebay and reprogrammed them but of course had the instruction manual so knew the make and model. If the car is working without the system you don't need to rush into it but if you can find the exact name of the system you should be able to source instructions and keyfobs. The system will not have been a full factory kit at a guess but more some kind of Scorpion/other brand unit fitted by dealers or aftermarket. Best to traul the internet/try a google image search of a pic just of the keyfob?

edit: sorry just saw above something things it is a factory bit of kit - at a guess it will still be a third party/ tier one supplier's off the shelf system stuck in the car - maybe try a merc dealer then ebay?!

Yep, looking through the options there's the OEM Merc route which looks like it could be over £200 or an independent saving circa £50 on that. Think I'll try one more set of new batteries first just to be sure.

[truck71]

So, new batteries work the alarm using the fob but not the central locking- any thoughts? Credit card type spare works both..

[truck71]

PositronicRay said:

Does the central locking work okay from the key?

You could try taking out the ecu's (boot I think) and connectors and re-seating with contact cleaner.

This has sorted all sorts of electrical gremlins for me, including alarm problems.

No, central locking doesn't work using the key, that said central locking is working with the credit card spare. ECU's a great shout- time to delve in the boot.

[truck71]

Sorted! Re syncronised everything now the new batteries are in the fob and all seems to be well.

Now to sort the slightly wobbly rear view mirror..

[truck71]

Old Merc said:

I`ve learned that these fobs like very good batteries,change them regularly.My alarm was playing silly buggers,lights in the mirror flashing etc and it was LOW batteries in the fob causing it. I always keep spares in the car.

Good advice, bought the set this week off amazon for £2.50 and will re order another lot as you suggest.