2007 Escalade, 6.2L AWD
This morning I fired up the car, drove about 4 miles and stopped at a gas station. Filled up the tank, got back in, turned the key and... click. No slow turnover or anything. It felt like the started was engaging, but had so little power it couldn't even turn it over slowly.
While I was puzzling over this, a very nice gentleman offered to jump it for me. Hooked up the cables, waited about 30 seconds, and it fired right up (though the first revolution was a little slow, which I've come to expect when jump-starting a car. Shrug.)
When I got it back home, after shutting the car off and unloading some stuff, I decided to try it again, and it started immediately. This worked four more times before I decided to stop bothering my neighbors by starting the car over and over.
Some weird observations:
When the battery was "dead," the sunroof would open, but the power windows wouldn't budge. Also, the rear hatch wouldn't open, but the glass panel would. (The glass opens independently of the lift gate, and the lift gate uses a motor to open and close, which would require more power.) Door locks worked.
Attempts to start it appeared to reboot the ECM / BCM / whatever. The needles did their sweep to the right and left, the DIC displayed its startup message, etc.
My son was watching a DVD. After getting the jump, it started over at the beginning of the disc, indicating to me that the unit had lost power.
I saw messages for "service charging system," "service stabilitrak," and others that I unfortunately didn't make a note of. These messages have not reappeared since jump-starting.
I thought the battery might have a dead cell or something, so I pulled it and took it to O'Reilly. They connected their diagnostic tool - a box about 12" x 8" x 2" with a crappy LCD on the front and some arrow buttons - via its attached jumper-cable-like-things. After about 45 seconds, the employee said that the battery was good.
So, here's my quandary:
If the battery is good, why would jump-starting work? Is it possible that the battery test was incorrect? The last time I had a battery tested, it was a "drop it off and we'll call you when the test is complete" process, not a quick diagnostic like this one.
Doesn't make sense to be the alternator as the thing ran fine for an extended period of time after jump-starting.
Why on earth would the sunroof open, but not the windows or rear hatch / gate / whatever it is called?
This is my wife's car, and I don't feel comfortable letting her run around with the kids without figuring out what the problem is first. I'd also rather not spend $200 on a battery if this one is good. (It's a Delco battery, OEM spec, but I can't find a date on it so I have no idea how old it is. We've had the car for a little over a year.)
The only semi-rational idea I've had is that there is a loose ground somewhere, and that connecting it to the other vehicle to jump start it provided a good ground. This seems really far-fetched as, again, it ran fine afterward.
Doubt it is related, but I recently (about a month ago) replaced both belts along with the harmonic balancer. I see nothing amiss in the engine bay. No corrosion on the battery terminals, harness appears intact.