Battery Control Module

[woodysl]

I think I am having a problem with the BCM on my 2003 year SL350. I have replaced the utilities battery but after just 2 weeks the central locking stopped working and had to access boot via emergency key. New battery only showing 12.1 volts, so charged it up and everything OK again. Engine start battery OK, no problems. It seems like a permananet battery drain problem or a BCM problem not allowing the battery to charge. I have had car for 14 years without a problem with battery drain, so I suspect the BCM , can anyone adise
1) where is the dreaded BCM located in the boot and how do I get at it?
2) how do I test it?
3) apparently new ones are no longer available? Is this true or does someone know of a supplier
4) does anyone do tests / rebuilds on these units if I cannot get a new one?
5) any other advice on a fix would be appreciated. I have heard of people using camper van split charge units as a replacement, but this would have to be a last resort,

thanks ian

 

[G7Wagen]

Hi woody

Have you tested the consumer battery (rear) with a Voltmeter while the car is running?
It should show between 13 and 14.5 v make sure the car has been running longer than 5 minutes as the BCM diverts charge to the starter battery for the first 5 mins.
A code reader will show any BCM fault.
If the car is not charging, it could be the alternator or the battery is bad, the glovebox light might be stuck on causing a drain, but also it could be the BCM.
With a low battery the central Locking might not work

An Indy will check codes if you don't have a code reader...

 

[oldguy57]

I think I am having a problem with the BCM on my 2003 year SL350. I have replaced the utilities battery but after just 2 weeks the central locking stopped working and had to access boot via emergency key. New battery only showing 12.1 volts, so charged it up and everything OK again. Engine start battery OK, no problems. It seems like a permananet battery drain problem or a BCM problem not allowing the battery to charge. I have had car for 14 years without a problem with battery drain, so I suspect the BCM , can anyone adise
1) where is the dreaded BCM located in the boot and how do I get at it?
2) how do I test it?
3) apparently new ones are no longer available? Is this true or does someone know of a supplier
4) does anyone do tests / rebuilds on these units if I cannot get a new one?
5) any other advice on a fix would be appreciated. I have heard of people using camper van split charge units as a replacement, but this would have to be a last resort,

thanks ian

Someone on here or the other MB forum had a problem with the SL350 bcm . It was repaired and wiring altered. Do a search - it was quite an enlightening thread,

Edit - was on the other forum. Thread "Living with an R230" Post 366.

 

[woodysl]

I'll carry out a voltage check as advised and see what the reading is. The battery is OK its only 3 weeks old. I'll take the bulb out of the glovebox light to make sure its not that which is causing the problem

 

[G7Wagen]

This guy shows you the issues

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[Ted]

No need to take any bulbs out.
Set your phone camera to record and see if the light goes out.

 

[woodysl]

No need to take any bulbs out.
Set your phone camera to record and see if the light goes out.

Good Idea!!

 

[woodysl]

Battery checked after a 5 minute run and showing 14.1 volts. Boot and glovebox lights checked using Ted's ace suggestion, both lights go out. Will try coupling a voltmeter in series to see if there is any current drain when everything is switched off. Watch this space.

 

[richard]

A 2003 SL may well have an old Tracker on it - the batteries were nicad and when old just heat up instead of charging (so constantly take current and run down the main battery. There are also old batteries in the alarm siren that can do the same thing.
R

 

[woodysl]

I've been away, so haven't had a chance to try the current drain check by coupling an ameter in series, but will do that today. The new battery is still losing charge, so there is definitely a current drain going on. I recharged the old battery and keep checking it regularly, it's still maintaining a steady charge, so it looks like I bought a new battery for nothing! I changed the alarm siren about 8 years ago, when it started acting up, so its not the original fitment from new. I wonder how long these systems last? There is no tracker on the car as far as I am aware. It would have to have been an after market fitment and there is nothing in the file of paperwork I got with the car 18 years ago to suggest that one had been installed.