Final answer:
The correct answer is option D: The vehicle will be disabled. The DEF is necessary for the vehicle's emissions control system to function properly, converting harmful gases to less harmful substances.
Step-by-step explanation:
If a driver consistently ignores the dash warning to refill a diesel vehicle with diesel exhaust fluid (DEF), the vehicle's computer system is likely to eventually limit the vehicle's speed to enforce compliance, and if further ignored, it may prevent the vehicle from starting. DEF is a crucial component in the vehicle's emissions control system, specifically, its Selective Catalytic Reduction (SCR) system. Without DEF, the vehicle cannot properly convert NOx gases into nitrogen and water vapor, which is key to reducing harmful emissions. This fluid is an integral part of newer diesel engine systems designed to meet stricter emission standards.
Vehicles such as plug-in electric and fuel cell vehicles do not require DEF since they have zero tailpipe emissions. Alternative technologies and better transportation planning contribute to the reduction of emissions and fuel use in broader environmental efforts.