When should the tailpipe smoke test be performed on a gasoline vehicle?

The tailpipe smoke test is conducted after the tailpipe emissions test to gather specific information about the vehicle's combustion process and to verify the presence of any hydrocarbons or pollutants that may not have been detected during the initial emissions testing. Performing this test afterward allows inspectors to target any unexpected emissions issues by examining the characteristics of the smoke produced from the tailpipe. This sequential approach is crucial because it enables a proper diagnostic evaluation of the vehicle's emission control performance based on the initial test results. Additionally, it ensures that any emissions failures can be accurately identified and addressed.

Testing after the emissions test allows for a more comprehensive understanding of how well the vehicle is operating in real-world conditions, and helps to isolate issues that may be contributing to higher levels of emissions.