All,

Firstly, apologies that this is going to be a bit of a long one – there’s a fair bit of background to go through alas.

Earlier this year I started having problems with the roof mechanism on the car. I decided to bite the bullet and took it to an MB specialist in the town to get it properly diagnosed and sorted around 3 months ago. The roof had got to a point where all I had was a flashing red light on the roof button inside the car and the red lights on the roll-bar switch were also illuminated.

After a couple of weeks of the car being at the place, the roof control module was believed to be the cause of the problem. Owing to the extortionate cost of new ones of these a 2nd-hand one with a warranty was sourced and promptly fitted to the car. We had movement!

Unfortunately though, there was still a problem in that the mechanism would not lock in to place or return the windows to their natural position. It was also noted at the time that the windows were not dropping upon opening the door as would be expected.

Further investigations and the window motors had to be replaced. One sourced in the UK, one sourced from the USA (as I couldn’t get one at a sensible price over here) and they arrived. Fitted and the windows came back to life and were working fine. However, the whole mechanism was still not functioning as expected.

I know that some work was done to bring the mechanism to life and, after some jiggery-pokery all is good and working. Well, we thought it was. The car is currently at a point where the roof works exactly as it should for 3 cycles and then, at the time the windows are going back up again, they stop around half-way up and won’t move beyond that. Trying to move them with the window switch also does nothing – they are just stuck there. The only way that they will budge again is for the battery to be disconnected for about 30 minutes – after that the system has “reset” and all works again. Until the 3rd cycle and then the windows stop half-way up. And so the pattern repeats…

Interestingly, a fault code is being emitted from the windows:-
“Side windows S21/9 down limit switch L”
“Side windows S21/8 down limit switch R”

But the confusion comes in that the car does not have down limit switches in the door – the limit switch is built into the motor. Which adds another dimension – according to Mercedes, the chassis number gives that the car should have limit switches in the door, but they definitely are not there. And at this point we are at a loss…

They have spoken with a main dealer to see if they had any ideas and, by co-incidence, they actually had a similar fault on the same model a few weeks ago. The issue was resolved on that one by replacing the Window Motors again with genuine Mercedes ones where the 2nd hand sourced ones (as with mine) were not working (overall symptoms were exactly the same and the same steps and replacements had been done as with mine – even to the point of saying it should have the limit switches in the door but didn’t).

I did ask if, when the testing is being done, it is being a down-up-down-up-down-up attempt (so the 3x movements all at the same time) or if there is a gap between them being done to simulate “real life” (so put the roof down, leave it a couple of hours, put it back up, leave it a couple of hours, put it down again, leave it, etc.) but I have been told that has been done already and, again, on the 3rd cycle it failed in the same way.

So, my questions / thoughts are...

- Why does it work fine for 2 passes and fail on the third, every time? Suggests a heating / shorting issue somewhere to me?
- Is replacing the Window Motors again going to solve the problem?
- How do we know it is not the roof control module (as I have been told the windows pass through that)?
- Has anyone else had similar problems in the past and know of any other options to solving?

Thanks in advance for any pointers / guidance.

Regards

Tim Watts

 

Post your vin number and I will have a look.
I presume your soft top module has 2 plugs ? NOT 3 like the older version.
Does the auto up and down window function work?
It's possible that it takes 3 cycles before it logs a fault code.
You should be able to read the hall sensor positions with the HHT.

 

Hi,

Thanks for the response.

VIN number is WDB1290672F120324. Although, as advised, already there are discrepancies between what the car has and what it is believed to have...

It is indeed a 2-port module - for info, the part number is 1298203226.

Auto up and down window function I assume you mean the auto-drop when opening the door - yes, that is fine until the 3rd cycle then all stops.

I have been told that the only codes being seen are the one as listed above - I was over with them yesterday and they gave me the print-off that I copied the info from.

Thanks in advance for any pointers.

Regards

Tim Watts

 

Sorry, should have added, window motor part number (drivers side) is 130821329 . Passenger side would be the opposite equivalent.

Regards

TMW

 

I will have a look tomorrow when I get to work. I am in South Africa so there is a bit of a time difference.

 

Cheers - any assistance greatly appreciated.

Regards

TMW

 

Hi,
I had a look on EPC and it does show window limit switches as valid on your vin.
The fact that S21/8 and/9 are showing faults I would say you need to investigate that circuit further. Plug2 pin 23 and 40 are the inputs for the window limits switches.
Have a look if they are in fact pinned to the Control module.

Good luck

 

Hi,

Thanks for the info.

The only concern is that, although the VIN listing says the limit switches should be there, they are not - the window motors are the later one that has the limit switch built into it.

Would that still apply in that case?
.
TMW

 

I agree yes, but why the fault code. the newer version has Hall sensors on the motor and the counter value is used to determine window position.

 

Cheers - will pass this on.

TMW