'94 R129 - immobile passenger seat & central locking

[E55BOF]

Now that the running issues are sorted :bannana:, time to get on with the rest; there's still plenty to do! The passenger seat does not move on the buttons, and (possibly not coincidentally?) the passenger door lock does nothing at all. The passenger door electric mirror and door puddle light are fine. The central locking works perfectly from the driver's door lock (blade key only - the fob is U/S, but the factory immobiliser has been disabled and an aftermarket item fitted, which works fine).

I suspect either a fuse(s) or door wiring fault. I don't have a fuse location chart for the car, so don't know where to start looking. Can anybody help?

 

[Doodle]

2 fuse boxes - one under the bonnet, one in the boot. Are the fuse guides missing from the fuse box covers?

The central locking is pneumatically activated, if the rest of the locking system is working then considerations are a disconnected air line or that the lock unit itself is broken - either one will probably mean getting into the door.

 

[E55BOF]

The central locking in the door works fine, but only when activated by the driver's door lock. I assume the central locking vacuum pump is triggered by an electrical signal when a door lock is activated? The passenger door lock does not lock or unlock its own door either; is it meant to function as a mechanical lock also?

 

[Doodle]

No idea on that one, my passenger door doesn't have a visible door lock.

 

[JCW1]

The passenger door lock does function as a mechanical lock, as does the boot. I know this because I often disconnect the battery and then manually lock the boot and doors.

I'm also pretty sure that the passenger lock (when using the key) activates the central locking also. I can check if it would help.

My fob does work sometimes but the lights on the lock always blink red whether locking or unlocking. It used to be red for lock and green for unlock.

Don't you just love these cars

 

[RichardF]

I think you'll find a micro switch by the door lock, it'll trigger the CL. All exterior locks operate in the same way mechanical/remote and CL.

Auxiliary fuse box in the boot for, windows, locking, alarms etc. These should be detailed in your handbook + a chart inside. Strangely they're not in PDF handbooks available on-line (I don't think MB trusted the Yanks with fuse information)

If you can't find the info let me know and I'll scan mine later.

 

[E55BOF]

I'm also pretty sure that the passenger lock (when using the key) activates the central locking also. I can check if it would help.

Don't you just love these cars

It would indeed help; I'd know for sure what should happen.

I expected that with a car over twenty years old with no history worth mentioning there would be some things where just getting the information would be tricky. I wasn't wrong. I still like the car, though...

 

[E55BOF]

I think you'll find a micro switch by the door lock, it'll trigger the CL. All exterior locks operate in the same way mechanical/remote and CL.

Auxiliary fuse box in the boot for, windows, locking, alarms etc. These should be detailed in your handbook + a chart inside. Strangely they're not in PDF handbooks available on-line (I don't think MB trusted the Yanks with fuse information)

If you can't find the info let me know and I'll scan mine later.

Thank you, Richard. I'll check the fuses in the boot, but I suspect the door card will have to come off to see what I find. I'll do the boot lock first, though; easier to access.

I only have the on-line copy of the handbook for the US market; I dare say MB hoped that in America only people so wealthy they just couldn't be bothered to check, let alone change, fuses would buy their cars. From what I've seen, some of the Gulf states are like that now...

 

[Doodle]

These should be detailed in your handbook + a chart inside. Strangely they're not in PDF handbooks available on-line (I don't think MB trusted the Yanks with fuse information)

I'm not entirely sure they included it in the 94/95 handbook for this country either.

 

[RichardF]

This is a scan from the relevant page.

If you haven't done already try to get a clone of the star manual, mine came from ebay for about a tenner.

It has all the wiring diagrams and diagnostic info, invaluable for trouble shooting.

 

[Dec]

The central locking in the door works fine, but only when activated by the driver's door lock. I assume the central locking vacuum pump is triggered by an electrical signal when a door lock is activated? The passenger door lock does not lock or unlock its own door either; is it meant to function as a mechanical lock also?

The passenger door lock, when operated with a key blade, should turn 90 degrees left or right to mechanically lock/unlock that door, if it doesn’t, then it may be seized and might benefited from some WD40

The passenger door lock may well be mechanical only and may not operate the CL.

Dec

https://www.youtube.com/watch?v=IZmsozrMVXY

[YOUTUBE]IZmsozrMVXY[/YOUTUBE]

 

[JCW1]

It would indeed help; I'd know for sure what should happen.

I expected that with a car over twenty years old with no history worth mentioning there would be some things where just getting the information would be tricky. I wasn't wrong. I still like the car, though...

So I checked and on my car, the CL is activated whichever lock I use with either the key or the fob.

This means that if the car is locked and I unlock the boot, then the doors also unlock.

 

[JCW1]

If you haven't done already try to get a clone of the star manual, mine came from ebay for about a tenner.

Hi Richard,

Thanks for posting the fuse list.

I have purchased a Star clone disc from the States but not being particularly computer literate I was put off by the installation instructions which seemed to suggest it would only work with a really old version of Adobe and that I would have to both uninstall the latest version and prevent Adobe updating in future.

Did you have this or did your version just 'plug and play'?

 

[E55BOF]

The passenger door and boot locks turn with the key blade OK, but nothing else happens; only the driver's door lock activates anything. ISTR when the battery was dead flat it didn't do anything at all either. Strange that; that all three locks do not function as mechanical locks.

Thanks guys; I feel I'm getting there. I'll know more when I actually start dismantling.

 

[RichardF]

Hi Richard,

Thanks for posting the fuse list.

I have purchased a Star clone disc from the States but not being particularly computer literate I was put off by the installation instructions which seemed to suggest it would only work with a really old version of Adobe and that I would have to both uninstall the latest version and prevent Adobe updating in future.

Did you have this or did your version just 'plug and play'?

No, not plug and play but the older version of Adobe is on the disc. The thing is the one I have won't work on the latest windows laptops. Fortunately I've a clunky old Vista Home Basic laptop for garage use. It doesn't connect to the web so no problems with auto updates

I think some of the guys in the states run Windows 10 and a "virtual" Vista desktop on the same machine, this works ok. Don't ask me how it's done I'm a luddite.

In lieu of an enthusiastic teenager, I've been known to beg favours from the IT dept at work (They think I'm very stupid but I always remember them at Xmas)

This is a good resource, not R129 specific, but nonetheless very helpful.
Model 124 Maintenance Manual Index

 

[E55BOF]

I see from the fuse decode that there are two 25A (E&F) fuses for the seats, but both described as 'driver/front passenger seat'. If by chance one feeds one seat and one the other, which would make sense, maybe the passenger seat problem is just a fuse (he said hopefully...).

So far as the CL is concerned, the knobs on the doors inside the car both operate the system normally, so it will be a linkage or electrical problem.

 

[E55BOF]

Fuse F removed - driver's seat ceases to function. Fuse E - no change. Both fuses are pretty new, so it looks as though they may have already been changed in the recent past. I knew it wouldn't be that simple...

 

[Doodle]

Switch pack or seat control unit is next port of call then. It's very unlikely that you'd lose every function from the switch pack simultaneous, but it's easy to check as they're just contact switches.

Finger of suspicion seems to be pointing to the seat ECU.

 

[E55BOF]

I was wondering whether the switch pack had a single live feed? If so, and that was duff, it would account for the problem. The door card will have to come off to sort out the lock anyway, and I'll find out then. I'm no electrical expert, but I have and can use a multimeter.

 

[RichardF]

Looks like a white and brown wire is a live feed from the controller to the switch pack. It should be 5v with the ignition on. You'll also find a brown earth wire.

Lets hope something's just loose.

If you need the controller it's under one of the seat bases. The bases come out easily couple of screws on the front then slide forward.