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Discussion Starter · #1 ·
My 2000 540i won't start. I have parasitic drain. The battery keeps getting drained by something that has gone awry in the electrical system. I have replaced the alternator, pulled the GPS/computer system out and it still won't start. My mechanic is so kind to me and has spent a lot of time trying to figure this out by unplugging everything in the car one by one and letting it sit to see where the drain is coming from. The battery is new. Actually, I have had three new batteries in the last five months (all covered by CAA/AAA). I am so frustrated and am thinking I am done with my car. However, it is in immaculate condition and drives so beautifully that it would be a shame to put it to landfill. Anyone have any ideas what it could be? I am at my wit's end at this point!
 

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I would connect a current meter to the battery and disconnect the fuses one by one while watching the current meter. Disconnect the board computer / alarm system last since these control other devices.
If the current is still high while all the fuses are off, go and check parts which have the 12V without any fuse. The starter motor for example.
It is also possible that the parasitic drain is not constant (for example a failing electrical system switches on something just for a specific period). If you measure the current of the battery and it is around ~3-4 A then your battery will be dead in 1 day.
 

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Discussion Starter · #3 ·
Dear Acoste,

Thanks for the information. My battery is usually dead within one day. My mechanic has pulled all the fuses one by one (and has not charged me anything as he has not fixed the problem!) and thought it was the GPS/computer/radio system. That is what he pulled last week and the car started two days in a row for him. I had the car one day and it died the next. I don't think my car likes my anymore! It is going back to the shop this am (after a boost) and I will ask him to check the parts that have 12V with a fuse and the starter motor.

I have checked my battery many times and the drain is what you said - -3-4 A - it could be intermittent. This is so frustrating. I have a son who swims at 6:30 am three mornings a week and I need my car to start.

Thanks for the advice.
 

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So your car doesn't start because its battery has insufficient juice and something is causing your battery to drain. Have you replaced the blower resistor thingy for the HVAC? I did this and it helped, do a search on the forum for a DIY. I still have a slight parasitic drain (doesn't everybody) and this is what I'm doing for now:

1. PriorityStart! "Monitors battery voltage and automatically disconnects any undesired drain on your system as voltage reduces when engine is off. Disconnect threshhold is factory set at 11.7 Volts." WHAT THAT MEANS IS IT TURNS OFF THE JUICE TO THE CAR WHEN THE BATTERY GOES BELOW 11.7v WHICH LEAVES ENOUGH JUICE TO START IT LATER - YOU FLIP A CONNECTOR OR TURN IGN KEY (DEPENDS) AND THIS GETS THE JUICE TURNED BACK ON TO THE CAR SO YOUR NOT STRANDED SOMEWHERE. NOTE: I DON"T CARE IF I LOOSE CLOCK, ETC SETTINGS WHEN BATTERY IS OFF, I JUST WANT THAT CAR TO START! P.S. WHENEVER A BATTERY FULLY DISCHARGES ITS REALLY REALLY BAD ON ITS USEFUL LIFE AND CAPACITY. TRY TO NEVER LET THE BATTERY DRAIN OUT!

2. CTEK trickler when the car is parked in the garage to maintain battery at full charge.

This is my solution until I have some time to go through and figure out the real culprit. :mad:
 

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Discussion Starter · #5 ·
Help my BMW 540i won't start - has parasitic drain

Thanks for the message! I had the blower motor disconnected last Monday and the car has been starting fine all week. My mechanic set up a very small manual switch by the front passenger seat for me to turn on when I need the heat. I turn it off when I turn the car off. If this works for the next few days - I will have the blower motor replaced. I have a decent and good mechanic. He doesn't want to replace parts that don't need replacing and he is conscious that my car is 11 years old (and immaculate) but there is a limit to what one will spend at this point. It is still a great car and drives beautifully. However, I do have this love/hate relationship with it when things go wrong. Don't we all? Thanks for the other advice too with respect to the trickle charger. Have thought about that as well.
 
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