Mixtli

Hi all. I'm new here, so please be gentle??!

I have a 1990 928 S4 with a problem somewhere on the window / sunroof side. The battery was being drained after a day or so and after a good amount of investigation with a multi-meter, I discovered that the extra draw disappeared when I disconnected the fuse for the electric windows / sunroof circuit. Since then, the battery has been fine and keeps a good charge. I believe there is a control module under the passenger seat (this is a right hand drive UK car) which I suspect is the culprit but before I go to the trouble of removing the seat, I thought I'd check with you guys. Any suggestions or tips? If I do have to take the seat out, how is it bolted in?

Thank you!

Jim M.

You can reach it without removing the seat (at least on LH drive cars). Have you checked the window and sunroof switches? I had a window switch stick on my 89GT many years ago.

Mixtli

Thanks for the response Jim. I don't have the thickest forearms in the world (or even my house )) but I can't get my hand under there at all. When the circuit is live, everything works perfectly well and there would be no evidence of any problems if the battery wasn't draining. As far as I know, the circuit should also be dead when the ignition is off?

Jim M.

Sounds more like a relay problem than the window control unit. Have you checked the glove compartment light, a common problem.

worf928

The '90+ window/sunroof control unit is a - these days - super common failure mode. I've replaced ... five? I think ... of them this year alone. They are all starting to die it seems. When it goes it has a parasitic draw of 125 mA.

If you pulled the window/sunroof fuse and saw your draw drop by ~125mA then the CU is the culprit.

The first time you R&R one it is easiest to remove the seat because you can see what you are doing. However, with the seat all the way forward and the seat bottom all the way up it is easy to R&R the module. It is secured by a bracket that has (IIRC) one Philips screw and one 10mm nut. Once the bracket is remove the control unit can be withdrawn enough to disconnect the harness plugs. You will also, likely, find a 'nodule' of black electrical tape. Don't worry about it.

You'll need a bit driver with a Philips bit to get the screw out, BTW.

EDIT: The CU is secured both by the bracket and some double-sided tape on its butt. Your tape may or may not still be sticky.

ROG100

I will have a new replacement controller available in a few weeks that will overcome all the issues. One of my own PET peeves with Porsche.

Red Flash

ROG100

https://rennlist.com/forums/928-foru...-040-00-a.html

928 618 240 00 does not exist in the Porsche system yet it is fitted to all cars from 90 to 95.
928 618 040 00 is available but you lose the control of the windows and sunroof when you try and close them using the key.
I have discussed this with Porsche by many means until I am blue in the face with zero recognition of the issue or the problem.
We have a new unit coming out that will give the original functions and more and get rid of the old and sticky relays.

ROG100

As reported on the other thread the 040 unit works but you lose the close with key function.