Which method is commonly used to test tailpipe emissions?

The 5-gas analyzer method is a widely accepted technique for testing tailpipe emissions because it provides a comprehensive measurement of the different gases that are emitted from a vehicle's exhaust. This method measures key pollutants such as carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), oxygen (O2), and carbon dioxide (CO2). By analyzing these gases, inspectors can assess the efficiency of the combustion process and identify potential issues with the vehicle's engine or emissions control systems.

The 5-gas analyzer operates by drawing a sample of exhaust gases from the tailpipe and analyzing it using various sensors that can detect the concentration of these pollutants. This quantitative data is critical for evaluating whether a vehicle meets the emission standards set by regulatory agencies.

While other options such as the OBD II scan method can provide information about the vehicle's diagnostic systems and emissions-related faults, they do not directly measure the pollutants being emitted from the tailpipe itself. Visual inspections, on the other hand, are useful for checking physical components but do not quantify emissions. Oil analysis is not related to tailpipe emissions at all. Thus, the 5-gas analyzer method stands out as the most appropriate and effective tool for assessing tailpipe emissions.