Just thought I'd share this, for what it's worth. Climbed into my '04 after a few days without driving it, turned the key and immediately saw something was wrong. Got a message that the DSTC was malfunctioning, then the brakes. Various warning lights on, and the clock was showing dashes. Tried to start the engine, but all I got was the sound of - what I imagine to be - a solenoid fluttering. The engine didn't turn at all. I had visions of calling out the stealers, and paying them a fortune to replace various three-letter acronyms, since my warranty and maintenance plan recently ran out.
Turned the car off and repaired to my computer to consult the oracle at volvoXC.com. Didn't find a complete match to these symptoms, but after reading similar posts I decided the most likely cause was that the battery had somehow become disconnected for a moment (the loss of time on the clock). Also possible that, even though I had instrument lights, there wasn't enough juice in the battery to turn the engine, although that wouldn't explain the clock (would it?) and I had no reason to suspect a weak battery until now.
Back to the garage, disconnected the battery in the prescribed manner (turn off the climate control, wait >5 mins after removing the key, disconnect negative lead first) and found the battery-lead clamps were, indeed, not very tight - but not exactly rattling loose either. Decided to charge the battery overnight, just in case.
In the morning I touched the + and - leads together, to re-set the car's brains (just in case) then reconnected the battery - again in the prescribed manner (key to position II, reconnect negative terminal last, lock and unlock the car), re-set the clock and... presto! Car started and drove perfectly! No problem with the climate control, sunroof or anything else. Didn't seem any more powerful after re-setting the brains, though.
As for the underlying cause, other than the not-very-tight battery clamps, the last thing I did before this happened was wash the car. I didn't spray water into the engine compartment, but I did vacuum under the seats, and I wondered if I might have shorted out a wire there. However, after I cleaned the car I had no trouble starting it to drive back into the garage. If there's a problem with the battery it will show up again, of course. BTW, can anyone tell me if you can use a deep-discharge battery in place of the regular one?
Just thought I'd share in case this helps anyone else...
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