2001 BMW 540i Battery needs constant recharge

CHEDLEY

MEMBER
2001 BMW 540I
V8
4WD
AUTOMATIC
93,000 MILES

My 2 years-old battery needs recharging daily. I took the car to the Sears battery shop for testin and they confirmed that the battery and alternator are working fine. They poointed to a possible battery drain or leak.

For some time, I have noticed that the locking mechanism in the front passenger door clicks every 20 seconds, all the time, whether the doors are locked or not, and whether the engtine is running on or not.
As I read on this board a similar problem encountered
(See "2001 bmw-530-battery-needs-charging" ,,,http://www.2carpros.com/forum/2001-bmw-530-battery-needs-charging-vt210460.html)
I concluded that that is the possible source of the leak.

Question: how can I confirm that the passenger door locking mechanism is indeed the source of the leak?
And if so, should I remove and replace the passenger Door Lock Control Unit to fix the problem?
Any other solution?

4 Replies

BLUELIGHTNIN6

MECHANIC
16,542 POSTS

Hello
Thanks for the donation.

If your door locks are powering every 20 seconds then that will definitely be a cause for draining your battery. For more information about electric draws, read the following link's information:

https://www.2carpros.com/first_things/why_is_my_car_battery_dead_over_night.htm

Are your power locks working fine even with the clicking noise?

Thanks for using 2CarPros.com!

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Saturday, January 24th, 2009 AT 12:52 AM

CHEDLEY

MEMBER
6 POSTS

Yes, the your power locks are working fine even with the clicking noise.
However, I just found out that the passenger power seat switch was locked, I unlocked it, and the clicking noise is gone.
I am recharging the battery and checking if it continues to drain overnite, but I think this may fix it.

Thanks for the info on electric draws, it was very helpful !

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Saturday, January 24th, 2009 AT 2:03 AM

DOCHAGERTY

MECHANIC
9,601 POSTS

If you still have issues with your car, there are several items to check when a key off draw occurs. There is a potted semiconductor device that controls the fan speed called the final stage, there is also a final stage unit controlling the auxiliary fan in front of the condenser that can fail and pull power with the key off and out. The maximum allowable draw is 50 milliamps after the car goes to sleep. Sleep constitutes all doors and lids shut, key off and is achieved after perhaps 16 minutes. If you have deep cycled the battery several times it might have an adverse affect on the lifespan of your battery, so my concern is that you have all the information you need to get the most out of your 540I.

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Saturday, January 24th, 2009 AT 11:22 AM

CHEDLEY

MEMBER
6 POSTS

The current battery being 4 years old, and has been fully drained and recharged a few times. So, I installed a new battery, and everything is working fine.

Thanks.

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Saturday, January 24th, 2009 AT 8:43 PM