This one's a doozy.
I went for a tiny road trip today (just driving around in-state on a beautiful September day).
The car unlocked and ran normally for me for the first 90 minutes. At that point, I stopped for gas, and I wasn't able to lock the car. Normally, I press the indent on the driver's handle to lock the door. No luck. So I tried the lock button on the keyfob, still no luck. Then I tried opening the trunk, and using the "close and lock" button. Still nothing.
Feeling exceptionally clever at this point (and not wanting to leave my car unsecured while I went into the convenience store), I pulled up the Volvo On Call app and used the app to lock the car. Success!
Five minutes later, I come out from the store, and the car won't unlock. Can't use the sensor plate on the underside of the door handle. Can't use the unlock button on the remote. Using the iOS app tells me that it has unlocked the trunk, but pressing the trunk release does nothing.
I know Volvo provides me with a key blade inside the keyfob for just such an incident. So I slide apart the key fob, and take the blade out. I insert it into the hidden cylinder under the driver's door handle. I turn it up, nothing. I turn it down, nothing. I turn it down, I turn it up, nothing. Now I may be starting to panic.
As a last resort, I pop open the other half of the key fob, remove the battery cover, remove the battery, and re-seat it. Somehow, *this* is the thing that fixes it. You work in technology long enough, sometimes the answer really is, "did you unplug it and plug it back in?"
Just to be safe, I replaced the battery in the fob, and my mini road trip was able to continue without further trouble.