300CE-24 Some frustration setting in ...

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ray_hennig

MB Enthusiast
Joined
Dec 1, 2008
Messages
1,205
Location
France
Car
MB 300CE-24 Sportline
Well, some degree of success. Injectors, great news. Battery drain, more clues but no progress.

I have a current drain through fuse 9 - fuse 9 only - all others removed individually with no change. About 400 mA.

I've traced it down to the comfort module but not beyond that. Why? Because I've unplugged one of the two inner plugs from the module and the current drain reduces to about 20 mA - perfectly acceptable.

So, what comfort do I now not have? The windows don't now go up or down with ignition off and door open. They do with the plug inserted. There may be other things missing but I haven't found them yet. The right-hand seat belt extender doesn't work but that stopped working after the first appearance of the current drain. Possibly related?

Doubtless, that plug leads to/from something. Either that something or the module itself is leaking current. When fuse 9 is inserted, the comfort relay in the fuse box switches.

For those who know these boxes intimately, I removed the plug nearest the front of the car - nearest the front of the rear seat under which the module sits. I'd like to get the module out and study the solder joints but I cannot, for the life of me, get the outer plugs off. How, in heavens name, do they come out?

Anyway, I'm having some fun making things work better and, slowly, making progress. It's great having a 23 year old car that responds to some attention.

As always, best to all.

RayH
 
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This may help a bit? thread explains how to remove the plugs to the convenience/comfort module .
W124 comfort window puzzle - Page 3 - Mercedes-Benz Owners' Forums
can confirm the convenience /comfort module is fed by the convenience relay powered by fuse 9 if that's of any help but fuse 9 feeds quite a few things

Thanks very much for that. The wiring is not exactly the same; it appears that mine has more (but similar) feeds to the comfort module.

The problem is that I spend most of my time in Paris and the car, well, doesn't. Also, it's an utter pain having the thing in Paris. And, of course, at this time of year, pressure is on to be mowing and strimming!!!

I'll have to make do with less "comfort" and less current drain until I have time to diagnose this properly. It's clear that the comfort relay behind the fuse box is powering something as I can here it switch when I insert fuse 9. And, to re-iterate, when one of the plugs on the comfort module is removed, the current drain reduces to 20 mA. The circuit diagram you kindly sent seems to be relevant in that it's concerns windows that I have lost with ignition off. But my feeling is that my coupe (belt extenders? etc.) has more associated with that plug.

Anyway, something to think about and many thanks again.

RayH
 
Door and boot lock micro switches faulty, can and do cause current drains on 124s.

Old thread but why not rejuvenate. Same problem but more time to investigate.

Rear window stopped working a few months ago. Removed, cleaned and replaced all 4 door microswitches and the window works again. I measured continuity before cleaning on the lower (not the interior light one) right hand (its a LHD car) microswitch and noticed very occasional reluctance to close circuit. Rear window now works.

Current drain (350 mA) still there on fuse 9. RH seat belt extender not working and neither is the autoclose of windows/sunroof when alarm activated.

Where will this endeavour end?

RayH
 
Old thread but why not rejuvenate. Same problem but more time to investigate.

Rear window stopped working a few months ago. Removed, cleaned and replaced all 4 door microswitches and the window works again. I measured continuity before cleaning on the lower (not the interior light one) right hand (its a LHD car) microswitch and noticed very occasional reluctance to close circuit. Rear window now works.

Current drain (350 mA) still there on fuse 9. RH seat belt extender not working and neither is the autoclose of windows/sunroof when alarm activated.

Where will this endeavour end?

RayH

Cleaned and lubricated RH belt extender with silicon lubricant and grease on nylon wheels. Flooded microswitches with contact cleaner and repeatedly operated switches. Extender now works much more quickly than the other side that I'll now clean up.

Excellent result.

However, current drain still there and the only thing that isn't working is the auto-close of windows/roof when alarm activated. Is this related to the current drain?

Cautious optimism for future efforts.

RayH

RayH
 
Instructions on curing current drains on W124 models:

1 - replace comfort relay
2 - that's it

Nick Froome
 
Instructions on curing current drains on W124 models:

1 - replace comfort relay
2 - that's it

Nick Froome

Ah, yes, but which one? There's the little cube relay under the bonnet and then there'e the 500 Euro job ubder the seat.

Which do we choose.

BUT, I made a discovery yesterday. When I was looking around the 500 Euro job under the back seat, I noticed a small device just behind it, connected to some pneumatic/vacuum hoses.

What is it? It's electrically connected to the 500 Euro job AND IT WAS WARM. It is conducting current!!!

However, when it is unplugged, I still have the 0.35 A drain through Fuse 9.

So, that little device MAY be linked to my current drain but does not, in itself, appear to be the cause of the drain.

Maybe it is failing to switch something else out and that is causing the drain.

What is it and what does it do? I've tried to find a photo of the bits under the rear seat but cannot.

All ideas gratefully received.

Best to all.

RayH
 
Think it might be the vacuum solenoid for the rear head rests- irrc they have to be raised manually but can be released by vacuum operators
 
Think it might be the vacuum solenoid for the rear head rests- irrc they have to be raised manually but can be released by vacuum operators

A good suggestion and one that crossed my mind today. I'll give further thought.

Thanks v much.

R
 
What is it? It's electrically connected to the 500 Euro job AND IT WAS WARM. It is conducting current!!!

However, when it is unplugged, I still have the 0.35 A drain through Fuse 9.

So, that little device MAY be linked to my current drain but does not, in itself, appear to be the cause of the drain.

Maybe it is failing to switch something else out and that is causing the drain.

What is it and what does it do? I've tried to find a photo of the bits under the rear seat but cannot.

All ideas gratefully received.

Best to all.

RayH

Still making progress.

This morning, everything was working except the auto-close of windows/roof with the door lock or remote.

I removed the convenience module and eased every relay open and squirted contact cleaner aggressively into each.

I then examined solder joints on both PCBs in bright sunlight and with a magnifying glass - the old eyes aren't what they were!

I spotted 2 joints that looked slightly dodgy but it was far from conclusive. I resoldered both which was tricky without the magnifying glass - only 2 hands!

I intensively cleaned the plug/socket contacts and reinstalled the module. We now have auto-close of windows/roof.

So, everything now seems to work but we STILL HAVE THE .35 AMP CURRENT DRAIN.

If something were not working I would have a suspect but I can't find anything now that isn't performing as it should.

I'm tempted to give up and just remove the plug to the module when I'm going to leave the car for more than a day or so. But giving up goes against the grain.

Baffled.

Any ideas what else I can test?

Best to all.

RayH
 
Spotted used comfort control module on leboncoin (French buy/sell site). Exactly the same part number as mine. 50€ delivered to the door.

Should be able to try it out during October so will report back.

RayH
 
What about the alarm system, might be the culprit?
 
If the replacement comfort relay doesn't fix things then like John
What about the alarm system, might be the culprit?
i'd investigate the alarm wiring next to as it's gonna make use of the comfort relay for things like total closure and be spliced into the central locking vacuum pump
 
If the replacement comfort relay doesn't fix things then like John

i'd investigate the alarm wiring next to as it's gonna make use of the comfort relay for things like total closure and be spliced into the central locking vacuum pump

OK, more progress. The "new" comfort module is now installed and EVERYTHING works, auto window/roof closure included. However, the 350 mA current drain still exists!!!

Now to think about the other things John and Grober kindly suggested. I suppose I'll unplug other things linked to the module and see what happens.

I also wonder about the 'ice cube' comfort relay. Someone (Television?) suggested that there was a diode there and that might be the culprit.

In the meantime, I can always unplug the module when I leave the car for more than a week. The only things that don't work are the auto-close, sunroof and window/roof open/shut door open/ignition off.

I did switch off the alarm during my tests and the 350 mA drain was still there.

Oh well, more time with the car at the end of Oct.

Thanks again to all.

RayH
 
IIRC the diode was a 'carry over' (from the 123) on early 124s and around '88 it was replaced with the small K24 relay along with some changes to door switches... less of them i believe as there used to be two switches on at least the drivers door with 123s/early 124s?
 
I did switch off the alarm during my tests and the 350 mA drain was still there.

Just be aware as I had an alarm issue (non M-B) and even switched off it still had a power feed. It was total closure and tilt sensing jobbie.
 
Just be aware as I had an alarm issue (non M-B) and even switched off it still had a power feed. It was total closure and tilt sensing jobbie.

Yes, thanks John. Will take note of everyone's suggestions over the next few weeks before I'm down here with the car again at the end of Oct. It's funny how my remote diagnostics (me Paris, car Dordogne) has born fruit over the years!!!

Best to all.

RayH
 

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