R129 window lowering function

[MD5]

Hi Peeps,

Is there a specific module which controls the window lowering function on the 129 SLs? I know the window operation is integrated with the roof system, but I am trying to isolate an intermittent, non usage fault, which is:

When opening the doors, the windows drop half way individually, instead of the usual half inch, and need to be reset to assume normal function. Once the car and roof have been used for a few days, it's fine and is no longer an issue, and this only happens after a period of non usage, despite being on a battery conditioner.

Am I right in thinking there is some sort of thyristor memory cell which may be the culprit, perhaps integral to the door sensors?

 

[Sp!ke]

Have you tried doing a window reset routine? Just press and hold the window switches (both) and go all the way down, then all the way up a couple of times.

 

[MD5]

Hi Peeps,

Is there a specific module which controls the window lowering function on the 129 SLs? I know the window operation is integrated with the roof system, but I am trying to isolate an intermittent, non usage fault, which is:

When opening the doors, the windows drop half way individually, instead of the usual half inch, and need to be reset to assume normal function. Once the car and roof have been used for a few days, it's fine and is no longer an issue, and this only happens after a period of non usage, despite being on a battery conditioner.

Am I right in thinking there is some sort of thyristor memory cell which may be the culprit, perhaps integral to the door sensors?

Thanks, Spike, I have to keep resetting them each time I get in and out of the car for the first day or so, then they are back to normal. I'm sure it's down to the battery level or some sort of memory issue, but the car is used infrequently at the moment. I'm trying to isolate which circuit or module controls this particular function, to stop me having to reset them after periods of non use.

 

[Ten elena]

Thanks, Spike, I have to keep resetting them each time I get in and out of the car for the first day or so, then they are back to normal. I'm sure it's down to the battery level or some sort of memory issue, but the car is used infrequently at the moment. I'm trying to isolate which circuit or module controls this particular function, to stop me having to reset them after periods of non use.

I have looked around for info on this myself the other day as one of the doors has developed a drop problem as well (opposite to yours though, it doesn't drop on opening), and apparently if the battery level is low, the drop function can get disrupted and windows need to be reset to resume normal function. Not sure if anything can be done to prevent it, so would be interesting to hear what others have to say.

 

[MD5]

I suspect that there is a little more to it than just battery level, as mine did it after a 45 mile jounrey, but after another reset, and then opening the roof a few times, it was fine.

 

[Sp!ke]

When you have your battery on a trickle charge, is the boot fully shut or is it left slightly ajar? I just know that the window reset doesn't work if the boot is open so wondered if there was a link there.

Have you checked your earth strap an battery terminals to make sure the connections are clean and tight? (just thinking aloud at possible things that could trick the ecu into thinking there is a low voltage)

What year is your R129 by the way?

 

[Sp!ke]

This post might be relevant in this thread Windows Auto Drop every time i open the doors. - Mercedes-Benz Forum

Another time I had trouble when I opened my door, the window would go down 2/3rds of the way. The reason for this was because one of the motor mounting screws had broken away and the hall sensor in the motor could not function properly because the motor was not secured tightly so it could not drive the window regulator gear. The soft top controller needs signals from the hall sensors/window motors to operate properly.The soft top controller could not open the front soft top locks and so the soft top could not work. I reckon the controller got confused. I replaced the motor and the controller worked straight away.

 

[MD5]

When you have your battery on a trickle charge, is the boot fully shut or is it left slightly ajar? I just know that the window reset doesn't work if the boot is open so wondered if there was a link there.

Have you checked your earth strap an battery terminals to make sure the connections are clean and tight? (just thinking aloud at possible things that could trick the ecu into thinking there is a low voltage)

What year is your R129 by the way?

Mine's a 96, and the boot is always properly closed. It had a new window motor and regulator in the o/s door earlier this year. There is a possibility that something may have come loose, but they were replaced by my local, trusted indy at a small fortune, so I hope not! I'll get this double checked when it's next serviced, as the o/s window is a tad slower than the other. The car has had a history of doing this for the last four years or so at the start of each 'season', but this could have been caused by the defective motor and regulator that were replaced. That said, once it's been used for a few days, it's fine, but I bought another 129 eariler this year, so this one now lives at the father inlaw's and has hardly been used and hasn't had a chance to get back into its routine.

 

[Sp!ke]

It does sound like the hall sensor in the motor sometimes cant count the turns.

Was the replacement motor genuine or aftermarket?

 

[MD5]

You could well be right, Spike, thanks again. I bought a new regulator and second hand motor - I only ever use genuine parts - still getting on for £400, iirc.