Is it true I was suppose to use Disengagement on hilly terrains like I was driving on Hume Fwy. I never disengaged a 4th gear before by pushing the button.
Thanks Oz Volvo team. 
4th Speed Disengaged / Shift Indicator Arrow Question
- Edited
Yes
Fourth gear is not necessary for speed less than 80 km/h
It unnecessarily allows shifting from 3rd to 4th gear wasting fuel and causing unnecessary wear of the transmission
The same goes for when towing, carrying high load or mountainous roads, you don’t want to be using 4th gear unless the engine is at a very low load. Which is why the overdrive cancel button is there to give you the choice