W211 Battery Drain/Short Circuit

[Brucy]

Hi guys,

Went out to use the car yesterday (having driven it 3/4 days ago) and it was completely dead so I had to have it broken into to gain access

The battery was replaced in February so that shouldn't be the issue but clearly the charge is going somewhere! I've plugged my MBII in and looked through the codes and the only one I can find which seems relevant is 'N27 (lower control panel control module) has Short Circuit' - before I start pulling fuses does anyone know (or have any pointers about) what this is likely to be?

Andy

 

[Major774]

You need to find the resting amp draw for a key off position, then let us know the reading.

Loads of videos on YouTube. It requires you to wire up a multi meter on the negative terminate side of the battery to get a reading.

 

[Alps]

When you say you had to break into it, did you not use the blade key to open the door instead?

 

[Brucy]

When you say you had to break into it, did you not use the blade key to open the door instead?

I don't think the lock on the door is working which is just fuel to the fire at this point, and something i'll have to have a look at.

I've just been out and measured it, with no key in the ignition it's drawing about 7 amps.

 

[Alps]

there are so many control modules in these cars, it's a little time consuming but it will be a. case of checking voltage draw on each fuse.

 

[W1ghty]

Lube and use your key locks twice a year

 

[Major774]

7 amps... awesome (super high drain), it should be something easy to find. You need to set up the car again with the multi meter hooked up on the battery. Also leave yourself access to the fuse boxes, then pull fuses and see which one lowers the amp drain on the multi meter.

 

[Dodipops]

7amp draw is mega. I’ve experienced one like that before and it was the auxiliary heater element on the block that was the cause. Not all cars had them though.
I’d be double checking your findings.
A 7amp draw would flatten a fully charged battery in a matter of hours.

 

[Brucy]

Thanks guys, I’m just waiting for a second pair of hands to save me running around to check every time I pull a fuse! I left the multi-meter on for a minute or so to try and discount any initial surges and it seemed to hold steady. I will check it again before pulling the fuses though

 

[mersum1es]

7A makes something hot if it is just one component... it equals almost 100W heating power

No aux heater in gasoline cars.

Remember each time fuse is put back, car wakes up (draw is couple of amps) and need to be wait 5-10 minutes before it goes sleep again, if it goes... but as far as draw is 7Amps, there is no need to wait.

 

[Brucy]

Thanks for the help so far guys - I’ve been able to have a bit of a play with the fuses today. The 7amp draw seems to be related to the amp/satNav and disappears after a minute or so to leave the baseline of around 1amp. Not sure if this is normal or not but we couldn’t get it much lower despite pulling all fuses.

We then locked one of us in the car to measure the draw with everything locked and it’s pulling around 200ma consistently. Removing the alarm fuse this then drops to ~100ma and is also less volatile so I’m suspecting that this could be cause - does 100ma draw seem normal or still on the high side?

 

[mersum1es]

60mA is 'official' limit.

How you measure it - clamp ammeter is quite inaccurate and 100mA is close enough

 

[Brucy]

60mA is 'official' limit.

How you measure it - clamp ammeter is quite inaccurate and 100mA is close enough

just using a multimeter so suspect there is a bit of wiggle room!

 

[Ted]

100mA draw will take around a month to flatten a fully charged battery, so no major concern.