Rear window goes up, but not down
 

The driver's side rear window on my 95 E320 cabriolet will go up, but it won't go down. Here's what I've done so far:

- I put 12v directly to the window motor. The motor works fine up and down; window goes up and down. No problem with the motor.
- I inspected both switches - front console and rear seat. The window goes up but not down with each switch. I took the switches apart - they look clean.
- The window goes up with all the others when I operate the cabriolet top. It will not go down.

This problem came all of a sudden. It didn't get flaky (intermittent) and then quit. I simply stopped working altogether. What else can I check? I'm beginning to think one of the relays is bad in the convenience control module.

I would try searching. If that doesn't help then you might need to find a schematic. Hopefully someone else knows what is wrong.

I have a 1989 190e, different, but related, so my experience may be relevant. The window wires break inside the pillar betwen the front and rear doors, just before they enter the rubber tube to the door. I don't know why. You would not think that there would be much flexing. Both sides had the same problem.

You can check for continuity between the front console switch and the rear door plug, if you have a wiring diagram. On the 190e, the wires have the same colour code at each end, so it is easy. Probably yours is the same. One is always hot (brown) as long as the front console switch is plugged in.

On the 190e, you remove the panels on the inside of the pillar, exposing a hole at the bottom. You can see the wires going up the pillar. You have to disconnect the seatbelt. The rubber tube is big enough that you can leave it, and work from the door, for the other end of the wire. The broken wires (I always found two, although you would only expect one) will almost fall out on their own. It is easy to solder in an extra length to bridge the gap, and cover it up with shrink tubing.

Good luck!

Andrew

If you are looking for Wiring Diagram, http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1995/E320/SYSTEM%20WIRING%20DIAGRAMS/5452.pdf

Did you have the symptom that the window went up but wouldn't go down. Also that neither switch would make it go down?

It appears the way the system works is when you ground the "down" wire from the "convenience control unit" that makes the window go down. So as a test if you could ground the appropriate wire AT the "CCU" then that could help point to the trouble.

Yes, the window goes up but not down. I can make it go down only when I connect battery power directly to the motor.

This is a convertible. There is no rear door and no point where the wiring would flex.

I have the schematic. It appears to me that to operate the window, the two wires going to the unit are the power feed and ground. These two are the electrically reversed when going the other way.

All windows are operated through the convenience control module. There are eight relays - two for each window - one up and one down. The down relay for the rear window operates when activated. It doesn't appear burned. If anything, it's the front window relays that look kind of burned. The convenience control module does have some light corrosion on it. I hate to spend $600 just on a hunch and see if this is the problem.

There is an added complexity to my system. The windows are also controlled by the power top system. But I don't think it operates in series with the other wiring.

If you have a schematic and you can inspect inside the CCU then you are in pretty good shape. Unfortunately you probably don't have a schematic of the CCU itself since it is not published AFAIK.

Reverser circuits can be a little confusing. I gave up teaching electrical troubleshooting over the internet. All I can say is you have a good side to compare to so that should help.

Well, I apologise for assuming that there would not be much change in 6 years. I just looked at the schematic. The horror! Maybe 1989 is as far as I can go, in terms of technology.

Andrew

That 1995 system is nothing. In '98 they put it all on a CAN bus with a computer at each window... When that quits there is not much you can do, just put in new parts.

The switch is bad- replace it

Rear window problem
 

I had a 94 E320 coupe. Not a convertable, but same window principal. And similar problem. I traced my problem to the child lockout switch. The button would work. Stay up or down as you wanted it too. But the contacts inside failed. No down power.
New switch. Fixed my problem.

Will one bad switch make both switches not work? Also, he reported that a relay activates when he pushes the down switch.

But you could still put the window up?

Update. It started working again. Since my last post, I took apart the relay that operates the LR window down function to inspect it and cleaned one side of each contact. It didn't work at first, but later in the day the window started working again, and has been working ever since. I guess the relay wasn't as clean as I thought.

I've posted before that many problems I've had on my E320 (and even other vehicles) have been traced to burned or tarnished contacts (e.g., seat heater module, seat belt presenter module). That's how I got my high beams to work again in March.

Anyhow, I've added CCM maintenance to my list for when my car is idled for the winter. I'll be cleaning ALL contacts, especially since both pairs of front window relays look heavily arced. Thank you everyone for your thoughts.