Does your window limit switch do anything?

[moroza]

I'm working on replacing the left rear window motor, and wondering why it failed in the first place. Incidentally, what failed is not the motor itself, nor the regulator, and not even the white plastic gear inside the motor - all teeth looked ok. I suspect the internal clutch, which I didn't even know existed, kicked the bucket.

While doing this I was playing with what's supposed to be the limit switch (wiring colors and location don't quite match what's in the wiring diagrams, but it's the only candidate), and discovered that while it was working correctly and connected to the right places, it doesn't appear to do anything. The motor, disconnected from the regulator, works both up, down, and full-auto down regardless of what position that switch is at (it grounds a wire from the GM). Full-auto stops after a few seconds, a good bit longer than the window would take to open fully.

So a question for anyone who's ever dealt with their power windows (or better yet, has doorpanels off the car at the moment and wouldn't mind investigating): does your limit switch do anything?

[shogun]

here is a German function diagram for the E32 ZKE, but the same on E34 http://www.e32-schrauber.de/bmw/daten/zke/bild11.jpg
Fensterkontakte (Fenster geschlossen) = window contacts, window closed
item 11 is all related to FH = Fensterheber = window, and SHD = Schiebe Hebe Dach = sunroof
http://www.e32-schrauber.de/bmw/s-zke.htm

[moroza]

Thanks, but that diagram still shows the GM as a black box, and doesn't explain the switches' function any better than the wiring diagram does.

[GregT53]

As you know, if the limit switch is not working then the motor will continue to push the glass until the gears strip. I replaced two regulators last fall and remember discovering that limit switch, if not connected to the car, resulted in the window motor not working. So, it seems that the motor circuit is completed through a connected limit switch. I was able to operate the motor using a battery jumper box and clips. Of course, this setup provided the necessary ground for a complete circuit. Not sure any of this is helpful to you, but that is my experience with these.

[Layne]

I recall learning the same thing. I believe it was in the rear specifically, can't remember if I tested the front. Pushing the switch does not effect the movement of the window in any way. I just assumed it was not a limit switch, and maybe something to do with locking or an alarm system wanting to sense that the windows were closed.

[shogun]

In general the gear should not strip, as there is an internal overload protection inside the GM, below I translate the part of the ZKE German info I posted the above.

Fensterheber und SHD:
Das Relais schaltet ab

-wenn laenger als 60 Sekunden ein Strom von ueber 36A oder
wenn laenger als 0.3 Sekunden ein Strom zwischen 36 und 60A oder (Ueberlastung)
-wenn laenger als 0.1 Sekunden ein Strom groesser als 60A fliesst (Kurzschluss)

Um die Laststromkreise TSH/ZV/ZS/FH/SHD sicher vor Ueberlast zu schuetzen, wurde zusaetzlich zur 30A Sicherung eine elektronische (reversible) Stromsicherung eingebaut.
Im GM wird der Spannungsabfall am RM gemessen, und je nach Spannungsabfall (Stromschwelle) unterbricht das Sicherheitsrelais den Laststrom .

Die Abschaltwerte der 30A Sicherung werden dabei nicht erreicht (diese wurden nur dann schmelzen, wenn ein Defekt an der elektronischen Sicherung vorliegt).
Die Ansprechschwelle dieser elektronischen Sicherung ist so gelegt, dass immer vor Ueberlast der angeschlossenen Steuerungen automatisch abgeschaltet wird.
Ein automatisches Wiedereinschalten erfolgt nach 60 Sekunden!!!!
Jedoch nur dann, wenn diese Verbraucher abgeschaltet waren bzw kein Kurzschluss vorliegt. Ein automatisches Wiedereinschalten kann 6 x erfolgen bei eingeschalteter Kl. 15. Diese Sperre wird aufgehoben durch Ausschalten der Kl. 15.
Um die Ausloeseschwelle beim gleichzeitigen Einschalten mehrerer Verbraucher nicht zu erreichen, koennen bei der FH-Steuerung gleichzeitig nur 2 gleichzeitig angesteuert werden. Werden mehrere Tasten gleichzeitig betaetigt, so werden nur die zwei ersten Befehle ausgefuehrt. Sollte bereits bei 2 eingeschalteten FH die Ueberlastgrenze ueberschritten werden, so wird ein FH abgeschaltet. Dabei haben die FH vorne Vorrang.

short Engl. translation:

The relay switches off

-if there is longer than 60 seconds a current of about 36A or if longer than 0.3 seconds a current between 36 and 60A, or (overloading)
-if longer than 0.1 seconds, a current greater than 60A flows (short circuit)

To protect the load circuits, TSH / ZV /ZS / FH / SHD from overload, there was installed in addition to that an electronic fuse 30A (reversible).
In the GM the voltage drop is measured at the RM, and depending on the voltage drop (current threshold) interrupts the safety relay is the load current.

The switch off values of the 30A fuse will not be reached here (it would just melt when there is a defect in the electronic security).
The threshold of this electronic fuse is positioned so that is always switches off automatically before overload of the connected controllers.
An automatic restart is only possible after 60 seconds!!
But only if these consumers were turned off, or there is no short circuit.
Automatic resetting can be made 6 times when terminal 15 is switched on.
This lock is released again by switching off the terminal 15.

[moroza]

Ok, now with further testing, I've found that the (micro)switch limits the motor's Up movement - with the switch thrown, opening a ground signal to the GM, continually holding down the Up arrow on the window switch results in the motor cutting out after a second or two. With the switch open (when the window is open), grounding the signal wire, the motor will continue to move up (with no load) as long as the switch is held down. Still, it seems the time given for the motor to stop closing the window is excessive. Furthermore, how does it know when to stop opening? Confused as hell about this system... I need to replace my regulator and want to make sure the electronics are working correctly.

[whiskychaser]

I think I have the same document which Shogun refers to. Section 11.4 says that there is a max of 1 second from the window hitting the limit switch to power being cut off. As I understand it, if that failed, the GM would trigger the power protection relay or the 30A fuse would blow.

[ross1]

Ok, now with further testing, I've found that the (micro)switch limits the motor's Up movement - with the switch thrown, opening a ground signal to the GM, continually holding down the Up arrow on the window switch results in the motor cutting out after a second or two. With the switch open (when the window is open), grounding the signal wire, the motor will continue to move up (with no load) as long as the switch is held down. Still, it seems the time given for the motor to stop closing the window is excessive. Furthermore, how does it know when to stop opening? Confused as hell about this system... I need to replace my regulator and want to make sure the electronics are working correctly.

After reading Shogun's post and my own experience with regulators my understanding is this; The GM is solely responsible for cutting power to the motor before an overload and that the limit switch tells it when it is acceptable for the motor be drawing more current, briefly, ostensibly to close the window tightly(?). Should the command remain to open/close(kids playing with buttons, etc.) once the limit has been reached the GM will shut down the motor after X seconds.
I believe as long as the GM has a open or closed signal from the limit switch when the window is indeed open or closed it will be fine. The limit switch isn't a "hard" limit that will immediately shut of the motor merely a notice to GM which is responsible for shutting off the motor. Needless complication, perhaps.

[moroza]

As I understand it, if that failed, the GM would trigger the power protection relay or the 30A fuse would blow.

Or the motor's clutch would fail, as appears to have happened here (but I have yet to take it apart).

the limit switch tells it when it is acceptable for the motor be drawing more current, briefly, ostensibly to close the window tightly(?). Should the command remain to open/close(kids playing with buttons, etc.) once the limit has been reached the GM will shut down the motor after X seconds.

...regardless of input signals. Ok, that makes sense. It's more important to close the window tightly than to open it tightly.

So it appears that my electronics are fine and the clutch just wore out? Alrighty then.

[GregT53]

Needless complication, perhaps.

Indeed, and we thought rocket science was difficult! You've got to give it to those German engineers. The need to overbuild knows no boundaries. That's better than cutting corners in my book.

[moroza]

That's better than cutting corners in my book.

And that's why all their waterpumps have metal impellers, door panels stay glued for decades, M62 chain guides never wear, and Touring hatch wiring is reliable enough to run a space station.

[Layne]

That's the difference between overthinking and overdoing.

[ross1]

And that's why all their waterpumps have metal impellers, door panels stay glued for decades, M62 chain guides never wear, and Touring hatch wiring is reliable enough to run a space station.

You forgot loose bolts meant to retain trivial things like the oil pump and rocker shafts.

[GregT53]

And that's why all their waterpumps have metal impellers, door panels stay glued for decades, M62 chain guides never wear, and Touring hatch wiring is reliable enough to run a space station.

Most cars that are 25 years old have been in the scrapyard for a decade. Repairing loose door cards is a minor annoyance, and maintaining mechanicals on schedule is not unreasonable. Every vehicle has its warts; the longer they stay in service the more warts will surface. On balance, the E34 is pretty solid.

[moroza]

Tell that to my '81 Yota Or a 70's-80's Benz.

Generally yes, a reasonably-maintained E34 is relatively solid at this age. And age-related problems are one thing, as are mistakes and warts (oil pump bolts, for example). But we're lying to our teeth if we ignore that a few corners were cut in Dingolfing back in the late 80's and early 90's. Though not as many as later.

I've said it before and I'll say it again, regarding German automotive engineers: they think Of everything, but they only think Through about half of it.

[XAlt]

That's the difference between overthinking and overdoing.

That's the difference between not learning your lesson and being cheap.

Or a 70's-80's Benz.

Oops my timing chain guides.

[GregT53]

But we're lying to our teeth if we ignore that a few corners were cut in Dingolfing back in the late 80's and early 90's. Though not as many as later.

Absolutely agree on the corner cutting with newer cars, including BMW. Annoyingly cheap plastic usage in hard to access areas like panoramic roofs is inexcusable.

All the manufacturers are having to get to price points that attract buyers so corners get cut. Even Tesla had to get into the $30K price range because depressed sales of their $80K S model.

One of the best things about owning older cars, especially the E34, is that they are much more DIY friendly. I'm not sure I'd trade my M5 for a newer model for this reason. Plus, they flat out don't look or sound as good!

[Onizukachan]

And that's why all their waterpumps have metal impellers, door panels stay glued for decades, M62 chain guides never wear, and Touring hatch wiring is reliable enough to run a space station.

Don't forget the relays are in the trunk so current has to enter and leave the gate twice to open the gate, and no manual release.

[moroza]

Actually, I rewired mine to remove three or four wires, by putting the relays in the lid.