I know this sounds crazy, but I have done this twice in the last 2 days. I think I have the steps down correctly.
1. Drive the car, park it, turn off the engine
2. Get out of the car and close the driver side door.
3. Go to the passenger side door - Not sure if getting to the door has to be done slowly - like 5 seconds
4. Open the passenger side door - not sure if the door has to remain open for a few seconds
5. With the passenger side door still open, press the lock door key fob button (middle one) twice quickly - Not sure if you need the two or 1 will do
6. Close the passenger side door - the little yellow light on the front right panel should blink but NO BEEP
7. Test the passenger side door and it should be locked. Also, check the driver side door and should be locked too.
Note: I have a Pop cabrio, so not sure if this is model specific. I have noticed the behavior lately because I am keeping my computer bag on the passenger's side, vs in the trunk. With snow dirtied streets, the back hatch is pretty messy. Today, I tried to watch closely on the steps I was taking. Can anyone else try this on your Fiat? What did you find? Any improvements you found in the steps?