[MikeGMT]

My (V90) is the same, rear activates but not the front. Looking at the manual it only states 'when there is a risk of frost or misting' but no clue as to what temperature triggers the screen. I had a notion that it may come on when the snowflake symbol appears in the temp; display (2°C > -5°C), but today when I went out in the car it was 2°C, snowflake was there but the auto front screen didn't come on, so that blew that idea away. I wouldn't worry about it, I've only seen mine come on a few times in 18 months of ownership, it will come on when the right conditions are met.