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      02-12-2012, 02:08 PM   #6

Drives: E92 320D M-sport
Join Date: Apr 2008
Location: belgium

iTrader: (0)

Originally Posted by m1bjr View Post
The DME will NOT drain a starter battery in 30min.
It's consumption is in the order of hundreds of mA.
Not quite. I agree it should not harm a healthy battery, my battery had already a problem, and this simply aggrevated it. But it's also not that simple. Atter switching engine off and closing the doors the DME goes into sleep mode in 3 steps:

1) first stage is when the start/stop light remains illuminated. Should go off after 30 seconds, or when closing doors/trunk/hood, 30 seconds after this. During this time about every unit in the car is alive, and it pulls 4 Amp from the battery. This is what i highlighted, if you hook up an OBD reader that stays on as long as there is data, the DME won't shut down either as it sees activity. This will then take exactly 30 minutes,upon which the DME shuts down anyway. And then the OBD reader too. But if say two hours later you open a door, trunk, or whatever, the DME comes alive, the the OBD reader too, and they go into another 30 minute round, instead of 30 seconds, again pulling 4 Amp all the time. Now 4amp in 30 minutes is only 2Amp-hr, and we have a 90 Amp-hr battery. But go into you car a few times and it adds up

2) second stage it will fall back to much lower Amps, and another time interval (i forgot these values)

3) Lastly it will go to the full sleep mode. If that would be hundreds of mAmp you couldn't park your car for two weeks. It should be 40 mAmp max, value kindly provided by BMW, but really around 20 mAmp. Mine is at 18-22 mAmp