BMW Repair: 1999 BMW 528i Intermittent electrical and startup failure, volt ohm meter, startup failure

Question
Evan,

Thanks for the prompt response.  I will have a meter in the car and measure the voltage and current next time this occurs.

Follow up question..

If the battery is indeed getting drained totally, how would I explain instances when once I opened the trunck manually with my key, the electric circuits came back to life again and the car started  normally?  That's what happens more than half the time (about 6 times in the past year).  I only had to jump start the car twice in that period.

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Followup To

Question -
I've owned my 1999 BMW 528i for the last 1.5 years and have noticed this problem intermittently.

Once the car has been shutdown, sometimes it won't respond at all.  The remote key won't unlock the car.  When I put the key in the ignition and turn the key, the dashboard won't power up and and car won't start.  No buttons would work.  I generally go to the trunck and manually open it with the key and all of a sudden, the electricity would come back on and everything would be fine.

I replaced the battery last year thinking it might be a low charge issue but that's not it.

A couple of times, the car doesn't start at all and I've had to get a jump start even thought the battery probably had enough juice (didn't have a meter to test it).

I took it to my mechanic and he measured the voltage at the battery and that's a nice 13.99 volt so its not the alternator.

Called the local BMW repair shop and they said they can't do anything unless the failure is reproducible and I can't reproduce it consistently.

Any ideas on what to check for and what this might be?  Its got me quite worried..

Thanks.

--Michael--

Answer -
Mike, you need to get yourself a Digital Volt & Ohm meter. Your battery is going dead due to a highter than normal amperage draw while the car is at rest. Measure the Battery voltage when the car doesn't start. The fact that jump starting the car works is proof that the battery is dead and incapable of starting the car. Usually if the battery is low on voltage you will still get dash lights and they flicker when cranking the motor. When cranking you'll hear the clicking of the starter solenoid. You are not getting dash lights or clicking so the battery is discharged and most likely no longer capable of holding a charge. You need a good mechanic to perform a Closed circuit current draw reading on your car. Your car can't draw more than 40 milliamps when asleep. Your car should go to sleep after 16 minutes (you'll know when the car is asleep when the orange LED goes out on the shifter console.) Measure amperage inline between the negative battery cable and negative post without loosing power. make sure the trunk is open but manually close the latch. Also open the pass. door and manually close the latch.
Wait 16 min. and look at amperage reading. You want it around 20 milliamps but 40 is the limit. Start pulling fuses in the glove box one at a time and recheck the reading and this way you will find the circuit responsible. A plugged in cell phone charger or aftermarket device wired into the car will cause an excessive draw. Good luck.
-Evan

Answer
Mike it may be an intermittently faulty General Module (Body Control Module). Next time before opening the trunk press the central lock/hazard light button in the center console. That button should be hot and work at all times. It is controlled by the GM. The LED on the gear selector is the key. If that light is on then the GM is awake and Remote key/central locking/pwr windows/alarm and other such body items should work. If it isn't turned on until you open the trunk then the other functions you have used haven't woken the GM up for some reason. Usually we have the opposite problem of can't getting the car to go to sleep. Try another input like opening a different door or popping the hood to see if that wakes it up.
-Evan