Quick overview of my issue.

Battery is 5 years old died during work hours on Friday,

Boosted fine.

Was dead again the next morning.

Boosted fine again and kept a charge during my errands I was running.

Later that evening went to go start it again just to let it idle and warm up. It's been -40 for the last couple of days and having the battery in the trunk away from the heat it never warms so it freezes easily. Won't crank but have good power. Lights, fuel pump, chimes and stereo work but it won't even boost. Starter makes the click.

Today replaced the battery and still won't crank. Again everything is working and has charge and just getting the click.

Decided to scan it and got no codes, Reset it anyway and the car starts fine.


I'd like to know what the issue was so I can fix it instead of running into these weird random issues. It's too cold to be working on cars outside.

Maybe the low voltage triggered something in the computer and it wasn't functioning correctly?

My mechanic Brother doesn't know what would cause issues like this. Seems like these cars start to have electrical gremlins after so many miles.

 

what did you use to scan it? a code reader will only pull generic engine codes, its possible there was a non generic code stored that you couldnt read, and hence why resetting made it start.

it sounds to me like your old battery just crapped out, and -40 is tough on things. are you plugging in your block heater? do you have a battery heater? i would consider those a must in -40 if you want any car to reliably start.

 

LNFs don't have block heaters.

 

I've got an oil pan heater on it. The last battery had no issues through 4 harsh Winters with no sort of heaters at all.

Resetting OBD codes won't reset the ones the scanner can't access. Didn't even have a check engine light.

The last battery had no issues through 4 harsh Winters with no sort of heaters at all so a fresh battery should of worked fine.

Something with the ECM just wouldn't let it start. Every other function worked fine.

 

if your using a generic code just because it doesnt read codes dont mean it wont clear them. the ecm has memory for codes and no matter what codes are there, when a code reader or scanner clears them, it clears all of them, weather it can read them or not. now im not saying it resets other modules, its only the pcm.

the starting system in cobalts is typical of a newer car. the key doesnt connect to the starter solenoid at all, the key sends a signal to the bcm, and the bcm then sends the signal through the clutch switch and to one side of the starter relay. the other side of the relay gets power from the pcm. if you hear the starter solenoid click it means all that is working fine. however the pcm and bcm both have protection logic built into them to prevent damage. essentially whats happening here is the bcm or pcm is detecting the voltage dropping too low when it tries to crank so it stops it from cranking. like i said before, you may have had a code you couldnt see in the pcm and clearing the codes got rid of the problem. who knows, maybe you had a low voltage code from the other battery, just unhooking the battery doesnt erase codes instantly.