Mercedes W203 Parasitic Battery Drain

[GT160]

Hi all,

Would really appreciate any help in tracing down the parasitic electric drain, Ive spent a lot of time narrowing it down but have not managed to solve/pinpoint the problem. Heres what i know so far using a multimeter, unfortunately I dont have any access to STAR .

I followed the process of locking doors, bonnet, boot so car thinks its locked, left for about 30 mins, removed battery negative, connect multimeter to battery post and to the removed battery negative clamp.

Total Drain is 400MA

Removed Fuse 8,9 from the rear and the myterious fuse 23 (still not quite sure what it does as the fuse diagram does not seem to make it clear and ive driven a week without it in and havent noticed anything??)

Removing all three fuses I have a lovely drain of only 60MA

I put fuse 8 back in drain + 70MA = 130MA
I put fuse 8 and 9 back in drain + 220MA = Total of 350MA
I put fuse 23 back in and drain is a further +50 = Total of 400MA

So then went off to search for the cause of the drain,

1) Fuse 8 belongs to alarm and central locking, so common fault appears to be the alarm so i unplugged the alarm and the drain from fuse 8 goes away , so a faulty alarm is most likely suspect, i tested and i dont think the alarm works anyways as i open the car from inside whilst locked and the hazards flash but no siren, so logic would suggest i change the alarm and the drain should go away?

2) Fuse 9 refers to the interior lighting, so i removed the dome light in the front to take a look. Everything seems to work fine with the dome light, the only thing im not certain off is whether the light actually comes on with the opening and closing off the doors, it seems to suggest it only does this when dark....where is the light sensor for these? Anyhow i thought fault module maybe and found a replacement used unit and thought i would take a punt at £10. Anyhow again everything seems to work, but the drain is still at 400MA

3) Anyone any idea what fuse 23 does.

Any help would be greatly appreciated, its not a problem as such as i have just been using the car with the fuses out but im restoring and returning the car to my dad and would like to make it back to perfect condition but we are both scratching our heads on where the problem is

Thanks in advance

 

[oldguy57]

Central gateway control unit. Not getting it on Star means you're really working in the dark to see what exactly the problem is. You can spend hours and waste cash by chasing these drains. A local indie should be your best bet.

 

[Petrol Pete]

Did you unplug the alarm at the siren behind the wheel arch ?

if you have electric seat(s) un plug them under the seat itself.

 

[grober]

Mercedes-Benz C-Class (W203) (2000-2007) Fuse Diagram • FuseCheck.com

Fuse box diagram (fuse layout), location, and assignment of fuses and relays Mercedes-Benz C-Class - C180, C200, C220, C230, C240, C270, C280, C320, C350, C30 AMG, C32 AMG, C55 AMG (W203) (2000-2007).

fusecheck.com

F23 can be the cigarette lighter -if fitted------burnt insulation on wiring?
I believe its on the central console-----

cigarette lighter socket replacement 2003 c240 - MBWorld.org Forums

C-Class (W203) - cigarette lighter socket replacement 2003 c240 - I am new to the forum, i did search prior to posting this. However, I was unable to find how to go about replacing the cig lighter socket. I looked at my console, and dont see how the thing comes apart. Is there a trick to getting...

mbworld.org

 

[GT160]

Mercedes-Benz C-Class (W203) (2000-2007) Fuse Diagram • FuseCheck.com

Fuse box diagram (fuse layout), location, and assignment of fuses and relays Mercedes-Benz C-Class - C180, C200, C220, C230, C240, C270, C280, C320, C350, C30 AMG, C32 AMG, C55 AMG (W203) (2000-2007).

fusecheck.com

F23 can be the cigarette lighter -if fitted------burnt insulation on wiring?
I believe its on the central console-----

cigarette lighter socket replacement 2003 c240 - MBWorld.org Forums

C-Class (W203) - cigarette lighter socket replacement 2003 c240 - I am new to the forum, i did search prior to posting this. However, I was unable to find how to go about replacing the cig lighter socket. I looked at my console, and dont see how the thing comes apart. Is there a trick to getting...

mbworld.org

Thanks for all the replies so far

What is the central gateway control unit, where is it and what does it do? I removed fuse 23 and it didn't really seem to affect any functioning in the car which confused me. I checked the 12 v charging point and it seems to work even when the fuse was unplugged so not sure it is that.

I unplugged the alarm siren and the drain went down but still drainnof about 250 MA from fuse 9 or the lighting control unit, I unplugged the interior lights the black plug to it and the drain goes away. Only thing I can notice is that the lights don't seem to come on and off with the doors opening if that gives anyone any further clues?

I think I might be chasing my tail here without a star diagnosis.

 

[grober]

YOU MAY HAVE A CANBUS PROBLEM? WHERE SOME OF THE UNITS YOU MENTIONED ARE NOT " GOING TO SLEEP" ON IGNITION SWITCH OFF

Controller Area Network CAN-B - MBUSA Technical Training

Controller Area Network CAN-B - MBUSA Technical Read more about control, module, door, connector, voltage and band.

www.yumpu.com

THIS IS A BETTER VERSION

Controller Area Network CAN-B - Car Logic Bulgaria preview / controller-area-network-can-b-car-logic-bulgaria.pdf / PDF4PRO

Preview controller-area-network-can-b-car-logic-bulgaria.pdf - 23 Constantly Active CAN B CAN B needs to go into a dormant state when the ignition switch is in the 0 position. EIS is the control unit in charge of

pdf4pro.com

 

[MrGreedy]

Alarm siren getting wet behind the front wheel is a common fault. Most disconnect it. May be additional wet wiring fault in that area?

With regard to lighting drain, my immediate thought was one of the door open/close switches. Test them all with a multimeter. Boot, doors, glove box, ashtray.

 

[Rory]

2) Fuse 9 refers to the interior lighting, so i removed the dome light in the front to take a look. Everything seems to work fine with the dome light, the only thing im not certain off is whether the light actually comes on with the opening and closing off the doors, it seems to suggest it only does this when dark....where is the light sensor for these?

I've always assumed it used the light sensor in the windscreen, behind the rear view mirror. If the car has rain sensitive wipers then that sensor (either combined or separate) is there too.

Alarm fault showed on a recent Star check on my car - I had the unit changed, although most people on here think that was mad! Had no idea it was faulty (car was in for an ABS fault). Be aware that a Star check may show a whole bunch of stored / current faults, which can be somewhat scary!

If you're disconnecting the battery frequenty do be cautious as W203's have a reputation for blowing the rear SAM (signal acquisition module) when the battery is reconnected.

 

[GT160]

Thanks all really good information greatly appreciated Any further help greatly appreciated

1. How do I test the door switches ?

2. How do I protect or limit the chance of damaging the rear SAM , I have heard they are a bit fragile and I was a bit worried when it was rear fuse 8,9 that it might have a problem.

3. Is there anyway to test the canbus central control module ?

Many thanks

 

[whitenemesis]

3. Is there anyway to test the canbus central control module ?

As mentioned earlier STAR diagnosis would be a good step and probably the only sure way of testing the canbus system

 

[MrGreedy]

1. How do I test the door switches ?

It would have to be getting to the terminals or the connectors behind the trim panel and testing for continuity/break when the switch is pressed (for each switch).

Not quick necessarily, but if you have a multimeter, at least it is free and only costs your time.

Before spending a huge amount of time on it, just make sure there is nothing else on that circuit, and if there is, check that.

 

[Stratman]

Further to Petrol Pete's reply (post 3), memory seats were my first thought. While you're measuring the drain current disconnect the seats underneath them and see what effect it has. Memory seats can develop a fault where they draw around 300mA, not too far off what you're seeing.

 

[Petrol Pete]

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

Accept third party cookies

Good old David the 'Car wizard' some of his content is unintentionally funny. He is very knowledgeable at the same time. he used in be in the US military, fixin' to fix Tanks y'all.

 

[Fastcar155]

Hi all,

Would really appreciate any help in tracing down the parasitic electric drain, Ive spent a lot of time narrowing it down but have not managed to solve/pinpoint the problem. Heres what i know so far using a multimeter, unfortunately I dont have any access to STAR .

I followed the process of locking doors, bonnet, boot so car thinks its locked, left for about 30 mins, removed battery negative, connect multimeter to battery post and to the removed battery negative clamp.

Total Drain is 400MA

Removed Fuse 8,9 from the rear and the myterious fuse 23 (still not quite sure what it does as the fuse diagram does not seem to make it clear and ive driven a week without it in and havent noticed anything??)

Removing all three fuses I have a lovely drain of only 60MA

I put fuse 8 back in drain + 70MA = 130MA
I put fuse 8 and 9 back in drain + 220MA = Total of 350MA
I put fuse 23 back in and drain is a further +50 = Total of 400MA

So then went off to search for the cause of the drain,

1) Fuse 8 belongs to alarm and central locking, so common fault appears to be the alarm so i unplugged the alarm and the drain from fuse 8 goes away , so a faulty alarm is most likely suspect, i tested and i dont think the alarm works anyways as i open the car from inside whilst locked and the hazards flash but no siren, so logic would suggest i change the alarm and the drain should go away?

2) Fuse 9 refers to the interior lighting, so i removed the dome light in the front to take a look. Everything seems to work fine with the dome light, the only thing im not certain off is whether the light actually comes on with the opening and closing off the doors, it seems to suggest it only does this when dark....where is the light sensor for these? Anyhow i thought fault module maybe and found a replacement used unit and thought i would take a punt at £10. Anyhow again everything seems to work, but the drain is still at 400MA

3) Anyone any idea what fuse 23 does.

Any help would be greatly appreciated, its not a problem as such as i have just been using the car with the fuses out but im restoring and returning the car to my dad and would like to make it back to perfect condition but we are both scratching our heads on where the problem is

Thanks in advance

Hi , me man that fits all electronic components on my car says on Mercedes the first thing he always checks on all cars is the earth on all cars he works on.

Mercedes put many layers of paint on the cars than can reduce earthing !

 

[GT160]

Thanks for everyone's help so far. I think I'm going to humbly wave white flags as I think I've gone as far as I can go.

Took it to my local mechanic to see if his SNAP on computer maybe able to offer any clues.... It recognises the car and checks for OBD codes etc of which there are none. But when I try to scan the front and rear SAM it doesn't seem to be able to communicate with these not sure if that's the software limitations or the car having a problem.

I think I would be guessing/ going in circles I will try the switches and memory seats incase but otherwise I think it's time for either a good autoelectrician or Mercedes specialist oh last ditch main dealer I haven't visited one of those in years!!!

Any recommendations in Exeter or near Devon, happy to travel for the correct person etc

 

[Petrol Pete]

My recommendation ? Do not take an MB of this vintage to any main MB dealership.

 

[MrGreedy]

Mercedes independent specialist all the way I suggest. Check they have STAR to do a proper interrogation of the car.

Can any members recommend a local specialist for the OP near Exeter?
My knowledge around the South West is a bit limited, so Steve at Avantguard Automotive in Bristol is my nearest recommendation (although not that near, obviously!).

 

[chic0821]

Not that it helps you, but it took an Auto electrician 3 days to find a parasitic drain on my Range rover. I thought the bill would be monumental, but was fine as he explained that they had to try something then let the car go to sleep in order to check it, then try the next bit and so on, so although they had it for 3 days they were only working on it for part of that time. Auto electrician is the way to go.

 

[GT160]

Thanks for the advice and recommendations so far, I was recommended a good autoelectrician by the mechanics and garage I trust and use, but he is on holiday until next week, so will wait until then to discuss with him about whether he will be able to help.

Im guessing avoiding the MB main dealership is due to costs or am i missing something else?

 

[chic0821]

I would doubt if the dealership would have an auto electrician, probably not enough work to justify him, so they would sub contract the work out then add their cut for the privilege of you dropping the car off to them