Wife pulls car out of garage into driveway. Sets p brake and leaves my automatic selector in R and leaves the car. The car then beeps three times she had the FOB in her hand. So the car was obviously telling us it was not in park. We put it in park and the green light on the ignition illuminated and so we left the car. 2 hrs later the car wont start and flipped out. The DIC says all kinds of messages (FOB not detected, service active handling, reduced power etc and the windows went down halfway and the up and the doors would lock and unlock on their own, We could hear all kinds of relays clicking and wurring. The car would not start so I dic the neg on the battery(BTW the lights seemed dim too) to reset computer but it did not help. Finally I hooked up a battery charger and after a few minutes on it it started and ran fine. The battery voltage once it started was 14.0. I drove it on the freeway for a while and it stayed from 14.0 to 13.8-9. I parked shut it off and held the ac down to get a volt reading of the battery and it was 12.4 so..........

..............WHAT the HELL just happened?

Is this the start of a computer going bad?
The car has had a tune, headers, honker for what that is worth.

 

You battery got low on voltage because you did not shut it down properly. Sounds like it was just fine after you charged it.

 

please explain why that would effect the battery?

 

Reminds me of the HAL 9000

 

I'm not a GM engineer. My best guess is that since you left the car in R when you originally tried to shut it down it never fully shut off. All of the C6 electronics systems continued to draw current from the batt. draining it enough to "freak out" the electronics when you tried to restart it without having enough current. What year is your car? On my 2005 you can clearly hear a distinct sound come from the steering column area when you do fully shut the car down.

 

When you don't shut down properly, all of the car's computer systems remain powered up. This is a considerable drain on the battery, which probably wasn't at full strength in the first place. So when you come back 2 hours later, battery voltage has fallen enough to cause the computers to go nuts (which they'll do when battery voltage drops below 11.5 volts).

Now if the battery had been fully charged, 2 hours probably wouldn't have been enough to discharge it below 11.5 volts. But I'm willing to bet the car hadn't been driven enough, or frequently enough, to leave the battery at full charge before your wife pulled it out of the garage.

 

friday a 5 hr drive
sat used all day
sunday used a couple times not far though
moday used in the am not far
moday night a problem
Think I got a gremlin

 

anyone else?

 

Probably the start of the battery going bad.

What year is your car?
Some '06 automatics have shown a 'DBS'-like syndrome with sudden dead batteries. Maybe not this sudden, but that might call for the BCM software reflash, which your dealer should have. But that might also wipe your tune.
Make sure they check your battery and charging system real good!

 

some advise I got was dont use the auto head light feature. It is hard on batteries. Since the car has only 6700 miles in 10 months the guy thought that could be giving me a weak battery. He had battery problems in his Lexus and that is what they rec. He did that and his battery problems went away. Makes sense. Thought I would pass it on.

Dove it this am checked the bat cold before start 12.0 V and when I got back it was 12.4 so?

 

No one that I am aware of is reporting battery problems with auto headlights.
But if your battery is already going south, the auto headlights will put that much more pressure on it at start up time, and could be the 'straw that breaks the camel's back'.

 

I am going to take a calming deep breath and watch things. While using the radio, it ejected a CD the other day while I was switching radio stations. I thought I hit a button by mistake but now I am not so sure. Probably a new bat wouldnt be a bad idea though.

 

I think you are worried about nothing but, it is your car feel free to have it "fixed"

 

C6400hp,

I cant have anything fixed because its running fine now. So if I took it anywhere they would think i am nutz. I tried to recreate the problem by shutting down while in R then getting out of the car and then after a minute putting it in P and then leaving it for an hour or two but it fired right up. The main reason I am concerned is for my wife who does drive the car. I dont want her to be stuck.

1)You could be right-improper shut down
2)could be a bat going bad
3)could be the negative terminal wasnt making good connection(why are they a slip fit only)I'll make another thread on that
4)Or a combo of 2-3 of the above.

 

Its probably because you have a 243 head one side and 799 on the other...

 

The more tech side of it is as follows:

In a traditional car the actual incertion and removal of the key from an ignition activates many other things in a start cycle. As you turn the key in the cylinder, it isnt just an off-on switch. There are stages to the start cycle and accessory cycle. To accomplish this same functioning on a keyless system, the GM engineers used the reverse and start button power down to turn off the PCM by timer if certain conditions were met. Some of them were zero rpm's, reverse, and a donw stroke on the start button. After a time-out it would then shut off the vehicle. Sliding the key out of the ignition would have done the same but that switching isnt available. On the auto's it has to be in park as one of the conditions to shut down the PCM.

As a general rule when the power down cycle causes strange electrical behavior such as with the radio and climate control systems, and the battery condition has been corrected, simply power down the system by disconnecting the battery cable and wait a few minutes. Usually upon reconnecting the battery, all systems return to normal. Been there/done that.

Good luck and let us know if it works out for you.

 

A freshly fully charged battery will read 13.8 volts due to what is called a surface charge effect. At 98% charge it will read 12.6 volts and the voltage tapers slowly and linearly from there to a full discharge voltage of 10.5 volts. So a reading before start of 12.0 volts is equal to a charge state of 71.4%. A reading after driving of 12.4 volts is a charge state of 90.5%. In other words, you didn't drive long enough to fully recharge the battery.

Note that the voltage at which the computers go wonky, 11.5 volts, is equivalent to a charge state of 47.6%. This is a relatively deep discharge for a starting battery. Normally, you like to see the charge state above 80%, or 12.2 volts. Deep discharges drastically reduce the life of the battery.

 

Buy an inexpensive load tester and drive your car for an hour or so, then check the battery with the tester.

 

Or have your dealer check it on there load tester. They tested my 06 and found a weak battery, good luck

 

drove it the am checked the volts 12.6! 98% charged! So far running great.