Power window gremlins

[260e3]

HI Guys

i have a much loved 260e w124. sept 1989 . unfortunately it has a couple of gremlins in the power windows.
they tend to just stop working at times - not for any particular reason that i can tell. sometimes it is just the drivers side rear - other times it is all . mostly i get stuck with them down.

having researched a bit on here i discovered i have a computer controlled set of windows - it does the "up windows" thing when you hold the key on lock - coolest function i have seen on a car for a while - owned the car for 8 years without knowing that :Doh: .

i am guessing the issues are most likely with the computer -is this common. are there any tests to check it
or do i just need to chase a newer one - ex c class perhaps?

thanks

[pastelgrey300D]

Check your fuses and your switches. I have had the same issue on numerous W126s - one car had power windows which were working intermittently - turns out the fuse wasn't blown but it had corroded and arced badly on the ends where it touched the fusebox terminals - there was a corona shaped hole burnt out where the fuse touched the terminals. This was causing intermittent power to the windows.

The power window switches themselves were also in need of repair - the contacts inside had burned and arced and were black. After filing them back to bright metal and lubricating the switch internals with vaseline, all windows worked perfectly. The combination of bad fuse connections and the dodgy switches meant that sometimes all the windows would work perfectly, sometimes none would work, sometimes they would go up but not down and vice-versa.

Before you go replacing computers etc, I'd remove all your fuses and thoroughly clean the terminals - i.e. sand back to bright metal with fine wet and dry sandpaper and then smear lightly with vaseline. Clean up or replace all the fuses - make sure the fuses are copper and not aluminium (this is what causes corrosion). If this doesn't fix it, try swapping the power window switches in the centre console and see if that makes any difference.

Another way to check is to remove the door panel, disconnect the wiring and apply 12v directly to the power window motor - this will tell you if it's a motor/regulator issue or a control/wiring issue.

Good luck!

[gjlockyer]

Hi 260e3,
I have a slightly later 260 - by 1990 they were rebadged as a 300E 2.6, so if I were to be sucked in by this rebadging trick, I could image that my car is way superior to yours!
Agree about the key operated window closure being a very cool ( and very handy) trick. A few months back I was in a car park, closing sun roof and windows with said trick, as the driver of some flash modern thing got out of his car the other side of me and caught the action. He asked me how I did it, so I had to unlock the car, lower a window, and demonstrate. "How old is the car?" he asked. When I told him he just shook his head in amazement.
I agree with pastelgrey's very good advice. While capable of cool tricks, Mercedes did some very strange things also - fitting aliminium capped fuses is one of them. I would urge every owner to change them to copper ones, only ensure that you use ceramic fuses not the cheaper plastic-bodied ones.
Also be thankful that our "old" switches can be easily pulled apart and refurbished. I've done a few over the years. All that's usually needed is a small flat bladed screw drive to prise things apart. From my experience: proceed slowly and over a white cloth on a cleared bench (if any small component drops out, you don't want to search the garage floor for it - you can guess how I know this!). Use wet and dry paper to bring contact points back nice and shiny. Often small ball bearings are used - you will need to hold them in place with a dab of Vaseline during reassembly.

[260e3]

thanks guys
i am fairly sure it is not the switches, if i switch the ignition on and off about a dozen times it comes good most of the time. it can stop working while driving and come good again at the end of the trip. they all seem to stop working together .

i did do a fuse box clean up a while back - not sure if i did all cu fuses though.

the other thing that has got me thinking - i have a leak in the rear window and it probably gets down behind the seat - where the computer is?

if i did need a new computer - which one should i get? - never seen one advertised?

also - what else does it control - i seem to have a warning light for that comes and goes too ( the one for the tail lights)

[benzy53]

Hi 260e
Please PM me. I'm taking a E280 apart with all four windows working perfectly. On another note, you mentioned the window closing
with the key, I know it is a very nice feature. But do know after closing the windows/sliding roof you can open all four windows by
holding the key in the open position. This only works is you used the closing function before hand.
benzy 53

[MMWA]

thanks guys
i am fairly sure it is not the switches, if i switch the ignition on and off about a dozen times it comes good most of the time. it can stop working while driving and come good again at the end of the trip. they all seem to stop working together .

i did do a fuse box clean up a while back - not sure if i did all cu fuses though.

the other thing that has got me thinking - i have a leak in the rear window and it probably gets down behind the seat - where the computer is?

It wont be the window switches, they are only switching logic level inputs to the "Comfort Control Unit" which is what has the high current switching capabilities built in.

Water leaking in the back window will be the cause, the unit is under the back passenger side seat base, the seat base is not hard to remove it has clippy things at the front bottom edge on both sides. Check for water ingress / corrosion and rectify the cause.

There is also relay K24 white plastic one centre row at the top back of the hidden section of the fuse box which is for the comfort control unit, if you have power seats you can swap its relay with this one to see if that is the issue. They are the same transistorised relays.

[260e3]

thanks guys. i will check you the K24 - i didnt see this on the wiring diagram. mind you i have the usa one..

some photos.
rear seat removed.

P_20170603_145149 (Large).jpg

computer - no water damage.. cleverly designed to be off the floor.

P_20170603_145146 (Large).jpg

this is the computer

P_20170603_150108 (Large).jpg

P_20170603_145201 (Large).jpg

not sure what this is - assume it is some kind of pump for the vacuum system - always wondered how it hold the vacuum for so long.

P_20170603_145210 (Large).jpg

[MMWA]

have you tested it again once removed and reinstalled ccu, if it works now it may of had oxidised terminals.

and yep the central locking is operated on every up and down motion by that pump, it sucks and blows in one unit - keep your mind out of the gutter.

[260e3]

i have tested it a few times. interestingly the drop windows thing works now.
it will stop working on the drive home and start again when i pull in the driveway. seems almost random.
but it does die from time to time. that relay seems a likely culprit. i will change it for the seat one and see what happens.
can you buy them new ?

thanks

[MMWA]

i have tested it a few times. interestingly the drop windows thing works now.
it will stop working on the drive home and start again when i pull in the driveway. seems almost random.
but it does die from time to time. that relay seems a likely culprit. i will change it for the seat one and see what happens.
can you buy them new ?

thanks

I cant find the part number for the relay, but I'd be pretty certain it's available new, hopefully has the part number on it. If it makes no improvement your going to need to try another comfort unit and failing that your going to have a wiring / ground issue to find. Being intermittent that is going to be a nightmare. I saw that there are 4 different part numbers applicable to comfort control unit too. I don't know what the differences are but i'd try get one that matches. I believe the differences are equipment levels possibly.

Stupid question, but have you replaced all the crusty original fuses and cleaned the oxidisation off the terminals yet? I listed a seller for quality ceramic ones in another thread. Cheapo plastic ones with aluminium fuse material should not be anywhere near these cars, they belong in the garbage.

[260e3]

not stupid on the fuses. did this on the w123 and also the 124 last year when this started. not sure if they are all ceramic and cu but most are.
i couldn't work out which fuse the comfort unit is off?

[compress ignite]

Access to MB's 2 CD service manual:

.startekinfo.com/Shttps://wwwtarTek/outside/12264/?requestedDocId=12264


From W124 FSM (Factory Service Manual) ETM (Electrical Troubleshooting Manual) [U.S.]


http://www.w124-zone.com/downloads/MB%2 ... ETM/ETM.pd

AND:

https://www.startekinfo.com/StarTek/out ... TM/ETM.pdf

It says (page) 136 But is also says (page) 144

N57 is called the convenience control unit (Comfort Relay) powered by fuse H and Fuse A
(There's also another fuse in the representation of the fuse box BUT I cannot read it's designation)

BUT there's also a K24 convenience RELAY powered by fuse B and Fuse 2

[260e3]

Thanks again
i got a chance to look in the relay box, and found i have different fuses to that noted above. i dont seem to have a k24?
see photos?
which one of these could be the culprit? ( taken them out and sprayed everything with contact cleaner.

P_20170625_144828 (Large).jpg[/attachment [attachment=2]P_20170625_144835 (Large).jpg

P_20170625_144845 (Large).jpg

a map of the ones in my car?

relays .pdf