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Sorry in advance for the long post, purchased my impala in January 2016 no issues. 6 months later in june I went on a vacation for a week and I came back and my car was completely dead. I decided this was my fault and I probably left something on. I then drove it for a few weeks and everything was fine. Went on another week long vacation this time having my friend start it every couple days. On the second day of my vacation he went to start it and it was again dead. This time I was sure to not leave anything on. Drove it for the next few months and it was ok. Now 12 months after purchasing the vehicle it is completely dead every 10 hours or so. I go to leave for work, dead, I leave work, dead. It has not died while driving yet. I have not done any recent mods to the vehicle and it has no aftermarket electronics except for I changed all the lights to LED immediately after I purchased the vehicle 12 months ago. The dealership tested the battery and said it was fine. I am wondering if anyone else has this issue or anyone has any guidance. I just cant believe this is happening as my car is fairly new. Thanks in advance.
 

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The dealership needs to find out the cause and fix it under warranty.
 

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They can do a parasitic draw test from the battery and see whats going on.
However, my guess is that the timer that keeps everything on in the car after you shut it off is sometimes staying on. Bad relay or switch or both. When it's supposed to timeout and shut everything off it does sometimes and other times stays on.
The BCM and everything associated with it draws a fair amount of current and will kill the battery pretty quickly. I know this as it happened to me while I had the XM playing while I was detailing the car one day. Took about 40 minutes and it was done.
As it's a intermittent problem it may be hard to find.

The dealer should really be dealing with this under warranty though. If that dealership cant find it then go to a different one or reach out to GM Customer Service who frequents this site regularly and see if they can help you with finding someone in your area that can.

The above being said........................

You can do the parasitic test yourself if you have a digital volt meter that will measure amps. I think ( IIRC) the acceptable draw is 50 milliamps. To test it would would have to hook your meter up and wait a few minutes for everything to go to sleep on the car. My understanding is that can take 5 or 6 minutes in some cases. You may want to start on the 20 amp scale and then drop down from there.

Here is a video as how to go about it. This guy is pretty good at what he does and his videos are usually very informative.


Good luck
 

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I had a parasitic drain on my LaCrosse. It was
flatbedded 3 times...They finally kept it for days..They found out the Onstar (even though I didn't have the service) was turning
on at night and draining the battery. They replaced the unit, never had a problem again.
Later GM put out a TSB stating that cause for
battery drain.
 

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Interesting......I had my battery dead after not using it for about 1.5 weeks. It started to get cold so I figured that was something to do with it but my battery was down to 2.75V so didnt think cold would drain it that low.

Good info, I will keep my eyes open for this issue. Any chance you know the TSB # associated with this issue?
 

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Interesting......I had my battery dead after not using it for about 1.5 weeks. It started to get cold so I figured that was something to do with it but my battery was down to 2.75V so didnt think cold would drain it that low.

Good info, I will keep my eyes open for this issue. Any chance you know the TSB # associated with this issue?
There was PIC4935D
In 2016 ...new one....PIC4935E

Good luck...
 

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Interesting......I had my battery dead after not using it for about 1.5 weeks. It started to get cold so I figured that was something to do with it but my battery was down to 2.75V so didnt think cold would drain it that low.

Good info, I will keep my eyes open for this issue. Any chance you know the TSB # associated with this issue?
Did you find the problem with the parasitic battery drain?
 
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