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Discussion Starter · #1 ·
I took my 2010 automatic cobalt into a transmission shop for troubleshooting. It has been shifting poorly in the lower gears and stalling at stops unless I manually shift instead of using D (Drive). At first they told me the battery was bad, which made sense since the car had been sitting a long while and I did have to jump the battery twice that day, so I picked up a new battery under warranty and dropped it off. The shop called shortly after telling me that the new battery also tested bad but only when installed in the vehicle. Tested outside of the vehicle it passes. They continued to tell me there must be an electrical issue and that I need to take it to another shop that could diagnose it. So now I am left puzzled about what could be causing the battery to test bad only when it is installed. The car starts up just fine with the new battery and as far as I can tell with a multimeter there is no parasitic drain which also makes sense since the car starts right up after sitting over night. Any suggestions in trying to troubleshoot this would be helpful.
 

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Get the diagnostics probed with a good code scanner not a cheap one. One that can read all of the modules on your car not just the engine.
Read the transmission control units’ parameters and see the transmissions live data.
Once done, then you may get some intelligent help.

“battery to test bad only when it is installed” seem a little lame and not a full story.
If the battery is good and new…it’s good and new.
Now once you install a battery into your cobalt, there will be a small drain, instantly and is expected.
One item is the trunk light, another are all of the capacitors in all of the modules and radios. But this drain is short lived and should quickly die down to milliamps to microamps.
With your car off! You should not have a large current draw.
 

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Discussion Starter · #3 ·
Well AAMCO transmission apparently doesn't work on electrical problems and for whatever reason when they go to make sure the battery is testing good it fails but only when they test it while it is installed so they were unable to finish diagnosing the transmission.

I have tested for a parasitic drain with the car not running but I found nothing and the battery does not die overnight so this is not the problem.

I feel like there is some kind of large drain on the battery but only while the car is running. I'm unsure how to test for that though.

Could it possibly be the alternator?
 
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