2009 chevy cobalt charging system problem.

[shanekromer]

Alright i have a 2009 chevy cobalt. Last year the alternator and battery were replaced. no problems. Recently ive noticed the battery light comes on in the morning. i drive it to the gas station leave it running 30-40 minutes later it goes off. it will come on periodically through the day but not as long as in the morning. I checked the volts the alternator puts out with my multi meter. ranged from 14.7 at idle to 14.83 at around 2000 rpm. seems high to me but let you be the judge. I did a diode check on new alternator its good. checked acid in new battery good. checked battery after car was shut off 12.7 volts. i let the car sit all night,, it starts right up no hesitation but battery light will come on i check voltage it is around 11.4 ish and after about 30-40 minute it jumps to its respective place around 14.7 again. I checked for a parasitic drain i had no luck. multi meter read 1.5 amps when placed in series i pulled the radio fuse dropped to around 150 Ma. let it sit all night same thing battery light on for 30-40 minutes then off runs great. i know the threshold for Ma is 50 Ma at rest i think the 1.5 was because the car was not asleep yet. I proceeded to blow the multi meter fuse by accidentally touching it to both terminals while on a Ma setting. I plan to buy a new one tomorrow to further investigate the parasitic drain. I was just wondering if anyone had any ideas on what it could be thanks.

[Stealthee]

Parasitic drain and the charging issue is a separate thing. As for 14.7 volt output that is about right. It sounds to me like you got a bunk alternator.

[Tech II]

Agree....bad alternator....should not be 11.4 volts.....

[tomj76]

Battery light is telling you that the battery isn't getting charged, but instead it is providing power to run the car electrical system. The voltage reading is telling you the same thing (11.4 v when running vs 12.7 v with everything off). My guess is there's a bad contact in the alternator when it's cold, but makes "good" contact after things warm up. Sometimes that comes from a cracked solder joint. Make sure you test the alternator "cold" so that you can tell if that is the cause and not something in the wiring.