Tricky Gremlin - care to speculate?

[Sloan]

I had the first problem of any sort with my 2003 S this past Friday, and boy was it strange! I'll try to keep this short, but not leave out any important technical details.

Drive car home for lunch - leave it in my garage, top up - nothing unusal. (less than 4 block commute home, so car was still 'cold' - and trip home had been quick & perfect). Eat lunch, get back in car, start as usual and back out of garage, but thought I noticed a 'clunk' when I put it in reverse, rather than usual smooth engagement. When I put the car in forward gear (manual mode, as usual), I get the dreaded "Tiptronic Fail" blinking indicator pattern - since I'm less than 4 blocks away and also have covered parking here at my office, I decide to 'limp' it back to the office. Pull in to my covered spot, turn car off - UH OH - car goes completely dead - not a light shining, not a window moving, NO response to any key functions, etc. - force my way out w/o breaking glass, can't close door - start to evaluate what to do next. Consult with this site, have 12v booster delivered (thanks dad) to try to power latch to get battery access. 12v booster does not have 12v accessory line out, so have dad rig one up to use regular terminals on. (12v plug with the bare wire ends at end of cable run). As I put the 12v accessory plug (not attached to anything at this point) in to the 12v outlet the bare wire left on very tip of those cables brush & I see a spark (whoops) - BUT car immediately comes back to life, and has been PERFECT since that time. Once I got back in to battery access, I confirm battery is high quality and less than 2 years old, and does fine under load testing. Alternator showing full charge capacity, and battery holding decent voltage.

Any brilliant ideas? I have not had any, but did get asked, what would happen if you pressed one of the remote function keys on the remote as you were starting the car? Since there's not a 'panic' button on there, I did not see how that could have done anything, but I do recognize that I could have been pressing a button on there as I started the car ...... (and I am not anxious to try to 'experiment' with that of course).

Now I'm afraid that it could happen again at any time since I have no idea what caused it. I now drive with that home-made 12v accessory plug in the car, just in case I need to intentionally short out the system again (I'm partially kidding - I would not have done that intentionally - but would consider it if this happened again. I figure this was the automotive equiv. to a "hard-reboot" of the computer - I'm just happy I did not make it worse).

P.S. While this did happen during a storm, I'm 100% sure that there was no lightning strike to or near the car - and it had been in my closed garage the whole time I was eating lunch.