Hi,

I am hoping someone has seen this issue or has a suggestion. I have a 2007.5 GMC 2500, 6.6 DMAX, stock parts.
Issue: When vehicle left for a couple of days truck just clicks over and over. Sometimes it will start but most times just clicks – starter not engaging. I can lift off and put back one of the Ground cables from a battery – doesn’t seem to matter which one, and the engine starts immediately. I have tried a number of different combinations and it does not seem to matter which battery. Sometimes I will remove the ground from the front one and no go but removing from the back one and putting it back solves the issue. There seems to be no pattern to this. I have cleaned all grounds on the batteries, both grounds on the block, the positive terminal fuse block located on the passenger side firewall and of course the batteries. Both batteries tested good (300Amps) 670CA each. They are AC Delco approximately 2 ½ years old – replaced on warranty by GM.
Once the vehicle starts it will restart every time for the rest of the day. The voltmeter guage on the dash reads above 14 Volts for the first little while then it settles at 14Volts.
I have tried just one battery at a time and had better luck with the passenger side battery than the front one. On occasion it still required disconnecting the ground or the positive and re-connecting.
Also, of note , is when the clicking occurs I notice that the dual zone climate control goes back to default (I think). I normally just use one zone but after the clicking both zones are active and the temp setting is at 74F. The radio is just fine though.