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W211 Battery Drain "Consumer Units" etc.

M

MBDublin

New Member
Joined
Apr 19, 2012
Messages
21
Car
E220 CDI Avantgarde W211
First post here - but have gleaned much useful information over the past 12 months which has helped tremendously on other problems.

Current problem (pardon the pun) The infamous parasitic drain - once a month get the "Consumers switched off" - trickle charge overnight problem goes away till next month.

Its still a PITA.

Decided to do some investigative work - got out my meter yesterday when I had some time to kill. Main Battery is only <12 months old, Aux battery < 3 months old.

Car Late 2002 E220 CDI Avantgarde

Opened up car, bonnet, boot & front doors, exposed fuse boxes in engine compartment, cabin and boot. Left car for 30 mins to ensure everything "asleep"

Disconnected negative from battery, wired meter in series - no appreciable draw as expected - battery takes a month to show consumers switched off error.

Reconnected negative cable and left car for a further 30 mins in case re connecting had woken up any systems.

Checked draw across every fuse in all three locations, three times.

Fuse No. 031 in the cabin has an intermittant draw of 60 to 70 milliamps.

Fuse chart shows this to be the fuse controlling fuse and relay box driver (works in conjunction with fuse 042 ?) which is the fuse protecting the Engine Control Module.

Without knowing exactly how this works - logically it makes sense that ECM powers up every now and then to monitor things.

However I'm also getting a 40 milliamp reading across fuse no 9 (located in the boot) - the fuse chart lists this as "Roof Unit" ?????

And I'm getting a 20 milliamp reading on fuse 22 (loacted in the cabin) - fuse chart says this is "Door control unit - passenger front".

Can't find a wiring diagram anywhere for the W211 so I have no idea what the roof unit is - guessing the lighting panel in front of rear view mirror.

I am assuming that a 120 / 130 milliamp draw every time var is parked up is killing battery. My drive from home to work is less that 2 miles each way every day and this time of year I would have Air Con on full blast, Heated Rear Window on, so battery re-charge time is limited.

Any thoughts, suggestions or ideas anyone might have for tracing and fixing these annoying drains would be most appreciated.

Thanks in advance.
 
Ammeter connected in series with the battery in order to measure the quiescent current, should be less than 30mA with all systems shut down.
If quiescent current exceeds 30mA you have excessive battery drain. Attempt isolation by pulling fuses.
Possible culprits include memory seats, comand, overhead control panel and boot lamp.
I guess the 'roof unit' is the overhead control panel, a known culprit.
I do have a workaround for memory seat controller should this prove to be the cause.
Good luck.
 
Thanks for the reply.

I don't have memory seat feature so I guess that leaves the Roof unit & the passenger door control unit.

Any idea what the "door control unit" is? - a new name for central locking??

As the roof unit is pulling the most - 40 milliamps I am thinking I might just pull the fuse to see whats not working and see if the battery drain disappears. Having seen videos of the removal of the roof unit I know that there are lots of ribbon connectors - anything special I should look out for in the unit?

Any thoughts as to where a wiring diagram for the W211 can be had?

Thanks again for your input.
 
donubenz, Savman, Mersum1es & Stan the Man,

Can't thank you enough for taking the trouble to post your suggestions and links. I will digest all the info and see where this leaves me.

I can see this is going to be a fun excercise - tracking down and tracing these faults.
 
Update 18/02/2013

I have to put the car through it's NCT(equivalent of your MOT) tomorrow so hand washed the car, polished the glass, hoovered out the cabin & boot.

Doing the later stages of above I had all the doors and the boot wide open for the best part of an hour - no key in the ignition.

Decided I'd connect my meter to see what the readings were and perhaps pull a few fuses. So set up - meter on milliamps reading -


Zip, zilch, nada, nothing. No draw across any of the fuses at all!

Oh this is frustrating.:wallbash:
 
keep your meter on and shut each one in turn to isolate the current drawing one.
 
donubenz said:
keep your meter on and shut each one in turn to isolate the current drawing one.
Click to expand...

That's part of the problem - a week ago with the doors and boot open I was getting a draw on three fuses when the car should have been asleep.....yesterday I was getting no draw on any fuses with the doors and boot open.

The only difference was that yesterday the doors were open to their fullest extent so as per mersum1es's post above I just wonder if there is some chaffing of the wiring going from the body to the door/ doors????

Interesting!
 
On my (2003) W211 the "roof unit" contains the lights etc but also an ultrasonic motion detector that motors down a few seconds after you lock the car.

Do you have one of those?
 
Satch said:
On my (2003) W211 the "roof unit" contains the lights etc but also an ultrasonic motion detector that motors down a few seconds after you lock the car.

Do you have one of those?
Click to expand...

Have to admit I have no idea :dk:

I do have a full Data Card that my local friendly dealership printed off for me. Any idea what code I should look for there to confirm that it is fitted / not fitted. My model is a 2002 E220 CDI Avantgarde.
 
MBDublin said:
Have to admit I have no idea :dk:

I do have a full Data Card that my local friendly dealership printed off for me. Any idea what code I should look for there to confirm that it is fitted / not fitted. My model is a 2002 E220 CDI Avantgarde.
Click to expand...

Few moments after you lock the car can you hear a brief "Whrrrr" sound?

Bend down and look at the roof units as that happens. With mine (an estate) an ultrasonic motion detector motors down from the centre unit.

Here is a pic. took just now through the window by torchlight!
 

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Satch said:
Few moments after you lock the car can you hear a brief "Whrrrr" sound?

Bend down and look at the roof units as that happens. With mine (an estate) an ultrasonic motion detector motors down from the centre unit.

Here is a pic. took just now through the window by torchlight!
Click to expand...

Just went out and had a look - no such refinements on mine.
 
Long Term Update

I have been living with this issue for many many months now and have done a lot more fault finding and research.

Every chance i got I would check battery voltages (static and engine running) - they were always within accepatble limits. I also checked battery drain and whilst this sometimes showed 60-80 milliamps immediately after engine shut off it soon dropped back to < 30 milliamps.

I tried these tests just after arriving home - an hour or two later, just before going to bed and 7 AM the following morning just before starting the car. Nothing showed up to suggest a latent drain.

Another possible fault to be investigated was the Aux Battery relay and wiring. It was suggested that the wiring can sometimes corrode and break. Logic suggests that if this cable were broken the error message would be constant rather than intermittent - however I checked continuity on the cables up to the aux battery and all was well. The Aux Battery Relay looks like an absolute pig to get at requiring removal of the wiper arm assembly followed by the protective shroud underneath.

Has anyone else had problems with this relay?

Or has anyone cured the Consumers off issue by replacing same?

I did notice that on my car that when the temperature dropped quickly overnight that I was more likely to get the "Consumers Switched Off" message. The car is not garaged and so is exposed to the elements.

I formed the following hypothesis:

Whilst a temp drop might cause batteries to be a bit more sluggish after an overnight of cold weather I couldn't rationalise a warning message especially when the batteries are fairly new and in good condition.

The Battery Control Module casing and it's earth strap are screwed / bolted directly to the rear valance. Perhaps there was a correlation between temp drops and the BCM sending spurious signals to the control systems?

So I went about thermally isolating the BCM. I disconnected the battery, and removed the BCM off the rear valance and moved it into the slot behind the battery. I made up an earth extension lead and bolted the BCM strap to it - reconnected to the original earth but wrapped the entire cable in insulating material. I then wrapped the BCM in insulating materials and wedged it between the battery casing and the bodywork.

This "fix" has been in place for the last 7 or 8 weeks and all looked good - until yesterday when the "Consumers Switched Off" appeared again. No significant temp drop so bang goes that hypothesis.

The one bit of research that shows a bit of promise is an MB software update to the BCM. This apparently delays the sending of voltage signals to the control unit for a minute or two.

Boy this has me frustrated! :wallbash:

Anyone who has a DIY update or cure for this problem - I would be most most grateful.
 
Main battery changed April 2012, Aux battery changed Aug / Sept 2012.
 
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