Confused with W124 IR central locking

300TDT

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E300 W124 diesel estate 1996, E300 W124 turbodiesel estate 1994, Golf tdi convertible,
My 'new' 96 E300D came with three IR remote control 'keys'. One works fine, operates the doors, arms and disarms the alarm, and starts the car. The other two had been sitting in a drawer for a while and had flat batteries. I put new batteries in the spare two and went through the procedure in the owners manual (point the key at the receiver and press the button - then stick the key in the ignition and turn it to 2nd position within 30 secs) but neither work.
I took both to bits (and have the blood on my fingers to prove it) in case the switch had come off/something unsoldered but both are fine. I've checked the IR beam using a digital camera and again both work fine (I should have done this first and saved some blood!). The metal keys will start the engine OK, it's just the electronics won't switch off the alarm/immobiliser.

I don't like not having a spare or I'm stuck with not being able to start the car if it's immoblised.

Any ideas please?
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television

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If the other keys have never been tried,,were they the correct keys for the car,,they came with 2 from new,,if they ar sending a beam into a camera , then they are working re the locking part
 
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300TDT

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Any of the three keys will start the car, but only the one remote will operate the c/locking.
Despite new batteries and the IR beam present, the two that have not been used for a while will not 'sync'.

If I can't get at least one of these other 2 remote controls sorted out, then I think I'll try and immobilise the immobiliser and remove the alarm, so at least I can get in through the passenger door and start the car if I lose my one working IR key.

I can't see anyone pinching a 13 year old diesel somehow!
 

grober

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If you have a digital camera do this test-take a picture of --or simply view in the camera display screen the key IR sender while pressing the operate button. If its operating correctly you will "see" the Ir beam as a grey/white flashing before the red test led lights up. The CCD sensors are sensitive to IR as well as visible light.
 

television

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As grober above ,I have put up a picture to test the beam.

You could also insert the key in the ignition and press any button on the remote to see if this will sync them
 

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grober

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You need to sync the keys to the car system.
My MB W124 handbook detailed a method involving the ignition switch only--IT DIDNT WORK!!
Another a method employs the passenger door lock on the coupe model but this should also work for the saloon and maybe the estate also?
This applies to the circa 95/96 models with the green/red LEDS in the drivers door lock position without the LEDS in the rearview mirror.
FIRST and important, best get new batteries for your remote. MERC seem to use 2 varta CR 2025 for the flip key type. Test the key is operating by pressing the button for a couple of seconds, a red light should show at the front of the unit after a slight delay If you have a digital camera and you view this indicator thro the camera LCD display you should see a white light instantly you press the button since the LCD will pickup the infra red signal.
NOW go to the passenger door and make sure the car is locked.

1.point the remote at the lock at a distance of about 12 inches. PRESS the remote for 5 seconds.
2.unlock the door by turning the key in the lock
3. wait 10 seconds then remove the key.
4.repeat 1. for 5 seconds.
5.lock the door with the key
wait 10 seconds and remove the key.

Your key should now be synchronised with the remote locking and lock/unlock the car.

Be deliberate in your actions. check which way to turn the key to lock unlock the car before starting. Take time between steps.
this worked for me
Other synchronising methods may work. I tried several before the one I detailed worked. best to try it several times with slight variations to the timing till it works. GOOD LUCK
 
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300TDT

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Thanks Graeme, yes I've done that using a digital camera, and both work OK. I don't know why they don't 'sync'.

BUT I don't understand this synchronisation process anyway - if by carrying out the 'syncing' the car knows what code the key wants to use (because I assume there is no feed back to the key) then how come more than one key will work anyway?

For instance if one of my IR transmitters wants to use a particular code, say, 'A178' and I tell the car that this is the number I want to use, how come I can ever use another transmitter which is bound to be on another code 'G654' or whatever? (without 'resyncing' to the 2nd key rendering the first inoperable.)
 
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300TDT

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Sorry Graeme my post crossed with yours.

Many thanks for your most recent I'll try that tomorrow.

Still don't understand how it works, but will be happy enough if I can get at least one more remote operating!
 
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300TDT

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Graeme. Success! - with remarkable ease.

I tried pointing the (not working) remote at the unlocked car both on the drivers side and on the tailgate, and nothing happened as before.

Now I simply locked the car with the key on the passenger side with a view to following your instructions, and, trotting round to the drivers side, I pointed the remote at the receiver and lo and behold it worked - instantly, and activates/ deactivates the alarm/immobiliser as well as the c/l.

Not sure why- but at least I now have a spare key, yippee!
 

grober

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success

Glad to hear it. How exactly this "synchronisation" process works in practice nobody seems to know. The method described in the owner's manual doesn't work for many people-don't really know why?? Many disappointed owners give up at this point but ad hoc methods like the one I detailed seem to work for many folks-thankfully.
 
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benrocker

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You need to sync the keys to the car system.
My MB W124 handbook detailed a method involving the ignition switch only--IT DIDNT WORK!!
Another a method employs the passenger door lock on the coupe model but this should also work for the saloon and maybe the estate also?
This applies to the circa 95/96 models with the green/red LEDS in the drivers door lock position without the LEDS in the rearview mirror.
FIRST and important, best get new batteries for your remote. MERC seem to use 2 varta CR 2025 for the flip key type. Test the key is operating by pressing the button for a couple of seconds, a red light should show at the front of the unit after a slight delay If you have a digital camera and you view this indicator thro the camera LCD display you should see a white light instantly you press the button since the LCD will pickup the infra red signal.
NOW go to the passenger door and make sure the car is locked.

1.point the remote at the lock at a distance of about 12 inches. PRESS the remote for 5 seconds.
2.unlock the door by turning the key in the lock
3. wait 10 seconds then remove the key.
4.repeat 1. for 5 seconds.
5.lock the door with the key
wait 10 seconds and remove the key.

Your key should now be synchronised with the remote locking and lock/unlock the car.

Be deliberate in your actions. check which way to turn the key to lock unlock the car before starting. Take time between steps.
this worked for me
Other synchronising methods may work. I tried several before the one I detailed worked. best to try it several times with slight variations to the timing till it works. GOOD LUCK

Excellent, tried a few different methods this one worked first time on a 1996 W124 - I now have a new (second hand) fob sync'd with the locks -
 

bigshineybike

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Did I read that right BENROCKER, you got a second hand key to work with your 1995/6 W124?
I found someone on ebay has what looks like the proper key for my car £20 for two. he has tested the IR led but cannot promise the keys will work with my car.
From what I can see there are lots of keys look the same but there is a 3 digit number screen printed in white onto the 'chip' inside the key.
since there seems to be a maximum of 999 numbers available and thousands of cars built there must be a level of interchangability?
Or is each transmitter and receiver actually paired up at the factory.
 

Naraic

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There is no interchangeability...each key is unique.
 

television

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As above and no secondhand key will work.
 

Tony 300D

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New member here, hello all, just been lucky enough to buy a lovely low mileage '96 W124 300D (non turbo) TE which has the same green/red LEDs in the door lock and no mirror LEDs. Similar problems to above. C/locking pump has just been replaced with a working secondhand unit which worked for a couple of days on the fob, but not this morning. Immobiliser kicked in and wouldn't kick out. Thanks to the info on this thread I've managed to get one of the fobs going at least in terms of disabling the immobiliser, but the central locking isn't working. Both our fobs had new batteries yesterday, but using the digi camera test I see that one is still not working. The new pump is definitely working (quite noisy aren't they!?). Car is booked in for Tuesday to try and sort it out. Very tempted to get them to lob the immobiliser into the skip, it's the only thing I don't like on the car which I bought for its old-school simplicity.
 

maxicab

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New member here, hello all, just been lucky enough to buy a lovely low mileage '96 W124 300D (non turbo) TE which has the same green/red LEDs in the door lock and no mirror LEDs. Similar problems to above. C/locking pump has just been replaced with a working secondhand unit which worked for a couple of days on the fob, but not this morning. Immobiliser kicked in and wouldn't kick out. Thanks to the info on this thread I've managed to get one of the fobs going at least in terms of disabling the immobiliser, but the central locking isn't working. Both our fobs had new batteries yesterday, but using the digi camera test I see that one is still not working. The new pump is definitely working (quite noisy aren't they!?). Car is booked in for Tuesday to try and sort it out. Very tempted to get them to lob the immobiliser into the skip, it's the only thing I don't like on the car which I bought for its old-school simplicity.
Hey Tony, it's over 4 years now, but did you end up getting the immobiliser removed from your '96 300D? Or maybe bypassed it? Can anyone advise on this or any other options? I think that it may be the best solution for my own similar problem ('94 Cabriolet with 880 and 551 codes). I also have the same green/red LEDs in the drivers door lock and boot lock, both of which are only very occasionally responding correctly to either of the original 2 key fobs - which as best as I can tell are working OK. I've tried a variety of synchronisation processes but nothing has changed. Of course I can still enter the car via the passenger door, but then can't start the engine as the immobiliser will not be deactivated. If I can manage to flukily get a door sensor to respond and get it started I'm too concerned to drive the car very far and stop or park it anywhere as the likelihood is high that I won't be able to start it again!
If immobiliser removal or bypass is not feasible, it seems unlikely to be a door sensor problem since both sensors are acting up similarly, but is there a downstream signal amplifier to which the two door sensors feed before sending signals to the immobiliser and alarm modules? I haven't found any of these modules but think the immobiliser is under the rear seat and the alarm has a ?K37 relay behind the dashboard. Does this all sound correct? Is there any chance that both the key signals are simply too weak, and that a new key from the main dealer would sort it out? I have been told that these IR keys are no longer available, but does anyone know better? People seem to have been able to buy them until around 2020.
 


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