On Monday, November 20, 2017 at 1:07:33 PM UTC, Jim GM4DHJ ... wrote:
lost a dippd beam bulb the other day .....only knew by the reflection from
the car in front....I thought canbus was supposed to warn you of this....or
is it just another digital thing that doesn't work properly ? .....

CAN bus is just a data bus to transfer sensor info etc. If the vehicle doesn't implement sensing for a blown bulb then you won't get a warning. So it's going to vary from vehicle to vehicle.