Final answer:
OBD-II has been standardized on all passenger cars in the United States starting in 1996, becoming a critical component in monitoring emissions and vehicle performance.
Step-by-step explanation:
OBD-II, or On-Board Diagnostics II, has been mandated on all passenger cars in the United States since 1996. This system is integral to monitoring a vehicle’s performance in regards to emissions and various subsystems within the car. While cars have gotten more environmentally friendly and efficient over the years, with measures such as the Clean Air Act requiring reductions in vehicle emissions, OBD-II plays a critical role in ensuring these standards are met.