Defect
On certain vehicles, a software problem could cause the backlight for the hazard light switch not to work, or to turn off while driving. As a result, you may not be able to see the switch in low light conditions.
Safety Risk
A hazard light switch that is difficult to see could increase the risk of a crash.
Remedy
Volvo Trucks will notify owners by mail and advise you to take your truck to a dealership to update the vehicle master control unit software.