E39 523i randomly draining battery - help!
Discussion
My E39 has randomly drained the battery (measured at 6.5V) on two separate occasions now.
Googling suggests that it could be the 'hedgehog' for the blower fan.
I checked the boot light and seems to be cold after the car is stood for a while so I've ruled that out.
Surely it's unlikely to be a dead cell in the battery, as usually it only drops by 2V or so when that's the case?
I've also checked that the fan is silent when getting out of the car - but I'm not sure if it even needs to be running audibly to drain the battery, when the 'hedgehog' is at fault?
Googling suggests that it could be the 'hedgehog' for the blower fan.
I checked the boot light and seems to be cold after the car is stood for a while so I've ruled that out.
Surely it's unlikely to be a dead cell in the battery, as usually it only drops by 2V or so when that's the case?
I've also checked that the fan is silent when getting out of the car - but I'm not sure if it even needs to be running audibly to drain the battery, when the 'hedgehog' is at fault?
To answer my own thread.
I removed the FSU (hedgehog) today and it was warm to the touch after the car had been stood for a couple of hours - so I guess I have found the culprit.
It was odd that it only seemed to drain the battery every couple of day or so, and not consistently every night.
New one ordered, hopefully it will solve the problem.
I removed the FSU (hedgehog) today and it was warm to the touch after the car had been stood for a couple of hours - so I guess I have found the culprit.
It was odd that it only seemed to drain the battery every couple of day or so, and not consistently every night.
New one ordered, hopefully it will solve the problem.
Dump the trafficmaster box in the boot too if you have that. But most likely the FSU. Pain to get the plug back on and the neighbours will think you're weird lying upside down in the footwell 
I think it's the little fan in the temp sensor in the heater controls themselves (behind the little grille, looks like a little computer fan) rather than the main blower motor that stays on, and as a result it keeps the k-bus live and stops the car going to sleep properly.
I think it's the little fan in the temp sensor in the heater controls themselves (behind the little grille, looks like a little computer fan) rather than the main blower motor that stays on, and as a result it keeps the k-bus live and stops the car going to sleep properly.
Edited by lufbramatt on Friday 17th March 12:17
The best way to find out for sure is to put a multimeter in series with the battery and see what current the car draws with the keys out of the ignition. As you remove stuff you'll see the drain go down. It will remove alot of guesswork with tangible figures.
But the FSU does sound likely.
But the FSU does sound likely.
The car had been standing for several hours when I removed the FSU and it (FSU) was hot to the touch.
My guess is that shouldn't be the case when the car has been locked for a couple of hours...
Just waiting for the replacement now.
ETA: Fixed speeeeling!
My guess is that shouldn't be the case when the car has been locked for a couple of hours...
Just waiting for the replacement now.
ETA: Fixed speeeeling!
Edited by TonyRPH on Monday 20th March 12:14
Gassing Station | BMW General | Top of Page | What's New | My Stuff