Need help I have a 2003 Grand Prix GTP the abs light was coming on and also the driver information center would flash O on every setting. The funny thing is when it sets all night and I get in it to go to work on the morning it does fine on my 20 minute drive to work but I don’t run the air in the morning. In the evening when I head home about 30 seconds after I turn the air on the abs and tcs light comes on then th dic starts flashing O. What does the air have to do with the DIC? Thanks in advance

Scan all modules for codes.

How old is the battery?

Is the alternator in good shape?

Yes the battery is 2 years old and both battery amd alternator check out good

Then yeah scan for codes as carfixer007 said above. Also I'd be curious what the voltage looks like when you are running the air conditioning . . . like not just a spot check but continuously with a real meter (not the in-dash one)

You said the alternator checks out good. What kind of check has been performed?

I used a battery tester at the parts store. Their is no voltmeter in the gauges just a light but the tester showed it charging st 14 volts

Does it still charge ~14v with all the lights on and blower motor on high?

You didn't test the battery you tested the charging system. You need to load test the battery.