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Discussion Starter · #1 ·
Hi, can anyone help, basically bought an e46 last week, the previous owner had probs with the battery draining, they said that it was the auto button on the digital heater display that was draining the battery as it won't turn off. The battery has drained twice on me in a week, I've noticed that it seems to be draining when the bonnet or boot is open longer for quite a long time approx 10-20 mins. It doesn't seem to be draining because of the auto button on the display, I do think it is something to do with the bonnet/boot been left open and if so what is it? I have had the alternator checked too and that is fine.
Would appreciate some help to save my pennies.
 

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Discussion Starter · #3 ·
Thanks for replying, I did try another battery, not a new one it was of my friend while I was waiting for my original battery to recharge, and it did kick in fine with that one, I left that second battery in for a few days when it drained again. This second battery worked perfectly fine on my friends car & has never drained. I just don't want to buy a new battery & it drains that one too.
Thanks Russ
 

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Discussion Starter · #6 ·
Thanks, will try this tomorrow, been googling a bit about the prob that the previous owner said they had with the auto staying on the heater controls and they thought that was draining the battery. Anyway found loads of probs on google with the heater controls etc and all refer to changing the final stage resistor and others say resetting the FSU. When using the heaters, if the 3 buttons on the left eg, blow on feet, face, front window are not on, the auto button light stays on and when I press the auto button it won't turn off. I did replace the heater control unit thinking maybe the button was stuck or faulty but still the same. Should this auto light go out and if so could this be what is draining the battery.
 

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I would check for a parasitic drain and start pulling fuses like in the link above, when the drain goes down you are onto the problem.

I've heard of the FSU draining the battery on e39s, check for any slight blowing from the vents when the ignition is off
 

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Also worth checking the wiring that passes from the body to the boot as wires can often become damaged:thumbsup

Have you noticed any other electrical problems?
 

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Discussion Starter · #10 ·
Will check today for the fuses etc, have noticed no other electrical problem apart from the indicators can have a mind of their own sometimes, they flash rapidly occasionally like when a bulb has gone, no bulbs have gone so presumed a prob with their connection.
 

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Discussion Starter · #11 ·
Have checked all the fuses just to see if any draining there was no problems with any of them, then tried the doors, bonnet & boot been left open to see if that did anything, when the passenger door or the boot is left open it does drain a small amount, not hugely and doesn't lose any more after a certain point so it can't be that either. Some fuses were missing from the fuse box so I did replace them, not sure if maybe that is the problem, will have to see how it goes.
 
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