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Cobalt 2.4 ecotech
Hey. So there is a bit of a battery drain somewhere in the car. I dont know where. Would love some ideas where to start checking.

Also its strange because the car won't start on a jump. I'll connect a good red top optima to the strut ground and positive post in the engine bay and the starter solenoid will click over a bunch of times but it won't send 12v to the start to get it started. I've even gone as far as to jump the 12v signal wire from the solenoid to the starter and it WILL catch and start but soon after sputter and die (immobilizer)

BUT if I put that same red top in the trunk it will start up and run fine. . . Super strange. I'm wondering if the immobilizer needs some kind of constant 12v from the rear of the car in order to work. i can't for the life of me figure out why it won't take a jump. its so weird.

any thoughts on this?
 

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I have an idea, check the big 50 amp fuse in the trunk near the battery for corrosion or to see if it's burnt, it appears crank circuit in your BCM isn't supplied 12 volts.
 

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is that on the positive loom in the trunk? I can see there is some kind of harness with a black plastic housing thats attached by a plastic gromet to a metal mounting point by the battery. that has to be it ja?

Also can you comment on the battery ventilation hose. i dont think its ever been hooked up. deffinitly not since the last battery replacement.
 

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Vent tube is to vent the fumes outside of the car if you have a lead-acide battery.
 

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Coby 7. Fuse is in great shape. Plugged a new battery in the trunk and she fires up no problem. put that old batter back in and try to jump it from the battery and no start again. That battery has to be toast. which is strange cause its less than 10 months old. Glad I got the warranty on it. Thanks for the help!
 

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Check your alternator by disconnecting the power lead to the alternator and see if the power sucking/draing goes away. I have a story for you... By the number of reports I've seen just like this one, I'd say this is a very common problem on the Cobalt!

This is a situation that happened with my daughter's Cobalt just this week. She arrived home and the car reported on the readout that it was "entering battery saver mode" or something similar. I did some searching and found out that this means that the voltage has dropped below 10.7 volts. This was strange because the battery is fairly new and she had no prior issues. She also reported a strange "whining" noise from under the hood. When she went out to start it a couple hours later, it was DEAD, DEAD, DEAD... As in deader than I've ever seen any car that has just been run a couple hours earlier. I put my heavy duty battery charge on it and it pegged the amp meter at 70 amps. This was truly a dead short situation. I've never seen anything like it. I charged the battery overnight and got back on it the next day to see if it would start, which it did. The whining noise under the hood was pretty easy to hear and the battery was being sucked dry again. I put a fresh battery in it from a different vehicle and again, dead short, heavy draw from the battery terminals. Huh... That's really weird. I started it again and I could smell something "plastic like" burninng near the alternator. I stuck my nose down there near the alternator and i could smell it even more and I could feel the heat coming off the alternator as well. The alternator was smoking hot... I couldn't even touch it. This was after just a few minutes of running. I used my lifeline... Called a friend who is a Pro mechanic and ran this scenario by him. His answer: Duh... Your alternator is toast! If you unhook the power cable from it, your problem will be solve immediately. He was absolutely right.

I've been working on cars all my life. I've never heard of an alternator doing this - Dead short, killing the battery and everything that goes with it. The car was completely dead and it could not be brought back with a 100 amp charger. Even with the charger on high, the charger could not overcome the shorting out of the alternator.

I've seen this same set of symptoms posted on Cobalt forums all over th place with no one seeming to come up with a solution. I hope this helps another Cobalt owner. The fix is pretty easy (test it first by disconnecting it though) Swapping out the alternator is about a 20 minute job and the part is $150-$350 depending on whether or not you go with a rebuilt or a new one. Rockauto has a new AC Delco for about $230 with no core charge. Not cheap but not horrible either.
 
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