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There I was, Sicily, 1918..
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2,531 Posts
Discussion Starter #1
OK, let's answer this once and for all -- I've been told that it's bad to disconnect the battery on the car. I've been told that it wipes all the stored memory (makes sense, since there's no power) and that it's bad for the car's computer because it loses the 'factory presets' like proper idle RPMs, etc... is there any truth in that? it seems unlikely, but I'd like to know, just to be sure. I know it'll lose radio station presets and such, and it'd probably have to re-learn your driving habits (no biggie either way).

Of course, I've also been told that removing the thermostat is a good thing (it's actually a stupid thing to do to your car) and that you should fill your tires to the Max PSI rating on the sidewall (also incorrect).
 

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dv8d
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204 Posts
Um I'm pretty sure disconnecting the ECU is not bad at all for your car. As you mentioned all you'll lose are your radio presets and seat presets, etc. I usually reset the ecu every mod I do to my car so the ecu can readjust itself to that mod, but then again I don't have a bmw.
 

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frequent tire purchaser
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668 Posts
I disconnected the battery on the 323 yesterday for 30 minutes to try and clear a SES light that's been coming on intermittently since I removed my MAS screens. The light was still on after I connected the battery and the radio presets were still programmed.
It's not bad to disconnect the battery.
 

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184 Posts

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Grüne Hölle Junkie
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1,656 Posts
on a related note.... my battery has been (or will be) disconnected for a year. my question is this: with the security code in the stock stereo still be saved or will i have to re-enter the code? and since i don't have the code, (it's packed up with my furniture) will the dealer be able to reset it using the VIN? :dunno:
 

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Registered
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163 Posts
I had problems with an E30

Everytime I unplug the battery, the tach goes crazy, I always have to plug and play with the fuses eventhough they are fine. It's a weird thing.

To the prev post, Yes the dealer can get your code with the vin.
 

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766 Posts
I disconnected the battery this weekend to install the Lightning DDE, had a lunch break, then reconnected the battery after two hours. All presets and settings remain the same except for miles driven since last fill-up returned to zero.
 

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Registered User
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1,115 Posts
i've disconnected my battery several times ( the last time was this weekend with the dde lightning install) the only thing that i noticed went out was the clock -- all the stations were there
 
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