2011 Sierra starting problems

dmccarley1979 · August 23, 2017

Got home at 1600 yesterday, attempted to leave at 1700. truck just clicked when trying to start it. left it sitting for a couple hours and returned to same problem. Hooked jumper cables to wife's car and still wouldn't start. left it on jumper cables for 15 minutes and hit the key and it started but very sluggishly. Thinking battery was drained, i left it running in the driveway for an hour to charge. Turned it off and immediately back on and it clicked. key off and back on and click. key off and back on and started but sluggishly. checked voltage running and have 12.96 volts. turned off and unhooked battery from truck and tested battery and have 12.64 volts. left unhooked for 30 minutes and hooked back up. hit key and clicked, off and on several times and started. but sluggishly.... turned off and back on started great. off and on started great. off and waited 15 seconds and started sluggishly. same thing this morning. also every time it starts sluggishly, the AC will set itself to strange settings. I leave the AC on auto and 71 degrees. it will change to auto off and 74 degrees with passenger settings off. twice it was blowing out of defrost when the settings showed dash vents. once it was blowing scalding hot air out of the defrost as if the heater was on. Lastly since this issue started the ambient temperature display on the dash was showing 55 degrees when it was closer to 90. this morning on my way to work it slowly crept back up to the correct temperature.

Any ideas before I go drop it at my not so trustworthy local dealership?

2017SierraSLT · August 23, 2017

Two words: battery cables.

They are a well known issue on the GMT900 trucks.

intheburbs · August 23, 2017

Take it to an auto parts store and have them check the battery and charging system. 12.96 while running seems a little low to me. Both my trucks are dead nuts 14 volts when running.

Battery cables/grounds, battery, alternator - one or more of those are the likely culprits.