S124 Central locking problem

[Rob77]

My S124 has just developed a weird problem. If I try to unlock the car, I can't do it at the driver's door, I have to point the remote at the boot.

I know what can cause that and its done this, intermittently, in the past. However, having unlocked, it now waits a few seconds then automatically locks up itself.

Another odd thing that came along with this fault is I can't open the rear hatch. The button doesn't want to push in to unlatch it.

Anyone have any ideas here please?

 

[carat 3.6]

The tailgate latch has jammed in the lock position, and is telling the vacuum pump to lock the car.

Try to unlock the tailgate with the key, or open it from the inside.

 

[Rob77]

The tailgate latch has jammed in the lock position, and is telling the vacuum pump to lock the car.

Try to unlock the tailgate with the key, or open it from the inside.

Brilliant, thanks! That sounds exactly like what's happening. I'll have a go at it in daylight when Christmas is over.

 

[Rob77]

Brilliant, thanks! That sounds exactly like what's happening. I'll have a go at it in daylight when Christmas is over.

And, indeed, that's what it was. Tailgate lock freed off and problem solved.

Well, I still have a problem with a faulty IR door sensor but the system now operates from the IR sensor in the tailgate or by key at the passenger side.

A new IR door sensor from MB is over £300 so I may have to get my own one repaired.

Alternatively, can anyone confirm if the IR door sensor is car/key specific or can I buy a working used one?

 

[Rob77]

Back to this one again: can anyone confirm if the IR door sensor is car/key specific or can I buy a working used one?

And also, is there a technique for removing the old handle assembly? There seems to be an Allen bolt or similar that just turns and turns.

 

[hotrodder]

I would've thought a used IR sensor would work but that's only a guess as all the 124s i've owned either had no remote locking or it was through aftermarket/dealer fitted alarms & immobilisers. I think it's only the control unit and remote that are matched and need coding or whatever?

The allen bolt is just a set screw and only needs loosening a few turns. To get the lock cylinder out (and/or take the handle apart) you need to turn the key to the right about 45 - 60° while sliding/forcing* the cylinder away from the handle i.e. towards the back edge of the door. It'll then come out. Similar deal with the door handle, slide towards rear edge of the door (to release the hook at it's front edge) and then it'll pull out

If you're not already aware of Mercedes Benz Model 124 - M104 Maintenance Manuals then somewhere in the door section is probably a better explanation of the above along with pics and the central locking section might have something useful about the IR setup

* may slide easily or may be stiff/put up a bit of a fight if it's not been removed in eons

 

[Rob77]

Many thanks, that's very helpful.

What's a set screw though? You mean it doesn't screw out but just spins round?

 

[Tim203]

Many thanks, that's very helpful. What's a set screw though? You mean it doesn't screw out but just spins round?

A set screw is a fastener threaded in its entirety as opposed to a bolt that is partially threaded.

 

[Rob77]

The allen bolt is just a set screw and only needs loosening a few turns. To get the lock cylinder out (and/or take the handle apart) you need to turn the key to the right about 45 - 60° while sliding/forcing* the cylinder away from the handle i.e. towards the back edge of the door. It'll then come out

My driver's door is remote only so I can't turn the key at all.

 

[hotrodder]

Skip the bit about turning the key then. The rear door handles don't have keys regardless and come out the same way, the only other difference being that the allen headed set screw* is more hidden than it is on front doors.

If it's too stiff to slide with just finger pressure than a piece of plastic (body filler spreader, old credit card, proper trim removal tools etc) slipped between the two parts of the handle to lever it back will do the trick. Or failing that a flat bladed screwdriver with tape over the tip

* aka grub screw in some circles for the type of headless fastener used to trap the lock cylinder in place. Pic nicked from http://www.starpartz.co.uk/products/mercedes-w124-series-right-side-door-lockkey.html but yours is effectively a blank/cover like rear doors by the sounds of things so won't have the 'prong' sticking out of it that the key turns

the set screw doesn't thread into the lock cylinder (only the door frame) it just jams the lock in place hence only needing to loosen it a few turns. The arrow in the pic is pointing at a lip which stops the lock from coming out until the screw is loosened enough

 

[Rob77]

I assume the part I need to replace is the part your arrow is pointing to (that sits alongside the handle and in front of the lock) with the opaque 'window' at the front?

Does anyone have a part number for it please?

 

[Rob77]

Skip the bit about turning the key then. The rear door handles don't have keys regardless and come out the same way, the only other difference being that the allen headed set screw* is more hidden than it is on front doors.

If it's too stiff to slide with just finger pressure than a piece of plastic (body filler spreader, old credit card, proper trim removal tools etc) slipped between the two parts of the handle to lever it back will do the trick. Or failing that a flat bladed screwdriver with tape over the tip

* aka grub screw in some circles for the type of headless fastener used to trap the lock cylinder in place. Pic nicked from http://www.starpartz.co.uk/products/mercedes-w124-series-right-side-door-lockkey.html but yours is effectively a blank/cover like rear doors by the sounds of things so won't have the 'prong' sticking out of it that the key turns
View attachment 58442
the set screw doesn't thread into the lock cylinder (only the door frame) it just jams the lock in place hence only needing to loosen it a few turns. The arrow in the pic is pointing at a lip which stops the lock from coming out until the screw is loosened enough

Hi, thanks, I've just been back at the garage. The problem is the set screw is set back behind a rubber bung on the door shut. The set screw should slide out using an Allen key but I'm told the Allen head is damaged and the Allen key just spins round without turning the screw.

The garage tells me there is no way to remove the set screw without destroying the door. Does that sound right?

 

[carat 3.6]

The garage tells me there is no way to remove the set screw without destroying the door. Does that sound right?

Hammer a splined key into it, or drill the middle out. No need to do anything to the door itself.

 

[hotrodder]

The garage tells me there is no way to remove the set screw without destroying the door. Does that sound right?

Nope, that sounds worrying... dealing with damaged/rounded fasteners is pretty much page one chapter one of being a mechanic. As said knocking in a slightly different tool into what's left is first step and splined/torx keys often work great in buggered allen headed fasteners
If the head is so FUBARed that doesn't work then you drill the thing out instead of cutting large bits of car off.

 

[Rob77]

The tailgate latch has jammed in the lock position, and is telling the vacuum pump to lock the car.

Try to unlock the tailgate with the key, or open it from the inside.

I got the tailgate latch freed off and all was well but it's jammed again. I'm going to look for a used replacement. Does anyone know what the part number is please? Or what actual part, should I be looking for?

 

[bolide]

The IR detector is just that - it's not coded or unique, it's just a detector. The one in the driver's door has a cable with an oval multipin plug attached and IIRC the tailgate one is similar

Nick Froome

 

[Rob77]

Freed off and working fine again. It seems to lock up in the winter, when it isn't used much but it's not broken.

 

[Rob77]

My central locking problem has changed. Since a couple of days ago, I'd lock the car and then after a while it would unlock itself.

But, as of this evening, I lock the car and 2 seconds later it opens again.

Help! I'm in Scotland and my car's parked up unlocked. There's nothing of value in it but it's a target for drunks and skunks!

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[roadhog]

That'll be one of the actuators extending and triggering the others.
I had the opposite problem recently, mine would lock itself. It turned out to be the driver's door actuator retracting at the slightest disturbance. They are supposed to stay either in or out until you activate the central locking, I'm not sure whether it's done via an internal spring or the external bellows.
Quickest way to diagnose which actuator is causing the problem would be to isolate them one at a time at the pump. Block of the associated line with a screw or similar and repeat until you've found the culprit.
If you're away from home and just want to secure the car until you return, unplug the pump electrics and lock each door manually.

 

[Rob77]

Thanks Roadhog. My car's booked into the garage on Weds to have the duo valve changed.

Unfortunately, I can't use manual locking as only the front passenger door has a manual lock.

What would an actuator cost? I'm wondering if I should be searching for a used one or if I'd just get the dealer to order.

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