A pretty easy "looking" job turned into a nightmare this afternoon. My 2011 DTS needed a new battery. The old one was tested in the car with an Altel 539B using the battery test function, and it showed that the battery was marginal (in terms of cold cranking amps). I hooked the battery to a tricklecharger for a day and re-tested; same result -- no go!
Yesterday evening i picked up a new battery with the intent of installing today. Since I didn't want to lose my radio, computer, and module memory settings, I opted for a "hot" swap using a memory minder cable connected to the OBDII port and hooked to an auxiliary 12V battery. This usually works very well and ensures for a good transition between the old and new battery; while keeping the system alive and functioning without problems.
Not today -- I installed the new battery and although the lights, windows, and radio worked fine, the car would not start. Fuel pump relay clicked, but no dash lights or functions available. Thinking I could pull some possible codes, I hooked up the Altel 539B, but it would not connect to the car's diagnostic functions. The thing was totally dead in the water -- so to speak.
I pulled the rear seat and used a 12V test light to check the fuses in the rear fuse box -- all seemed OK. After an hour of frustration, I got out the PowerProbe and tested every fuse in rear fusebox again -- this time the PowerProbe hit the #13 fuse as being blown. That #13 fuse is marked as the PassKey fuse, and which I assume is part of the anti-theft system. I pulled it, and it looked OK. Then took it to the bench and used an OHM meter to bench test it -- not OK! Very strange indeed.
Finally replaced the fuse and the car started up as usual and all the settings (radio stations, seat memory, etc. were intact). A two hour ordeal because of a failed or misdiagnosed 12V test light result.
What really intrigues me is what made the PassKey fuse blow during this entire procedure. I was super careful to avoid the possibility of a short to ground situation when hooking up the auxiliary battery for the memory saver, and when removing the old battery.
Lesson learned -- even when being pro-active, "Murphy" is still out to get you; even on the most simple of tasks.