Which system in a vehicle controls emissions?

The exhaust system is primarily responsible for controlling emissions in a vehicle. This system includes components such as the catalytic converter, muffler, and exhaust pipes, which work together to reduce harmful pollutants produced during the combustion process. The catalytic converter plays a critical role by converting toxic gases like carbon monoxide, nitrogen oxides, and hydrocarbons into less harmful emissions before they are released into the atmosphere.

While other systems, such as the fuel system, can influence emission levels by ensuring efficient fuel delivery and combustion, it is specifically through the exhaust system that the control and reduction of emissions are achieved. The cooling system manages engine temperature and does not directly impact emissions, and the suspension system relates to vehicle handling and ride quality, having no involvement in the emissions control process. Therefore, the exhaust system's significance in managing and reducing emissions makes it the most appropriate answer to the question.