What is is IM-240 testing?

Answer 1

I/M 240: Stands for "Inspection/Maintenance", an "enhanced" emissions testing program with a tailpipe test that lasts 240 seconds. The test is done on a dynamometer to simulate actual driving conditions. The vehicle is put through a "driving trace" as it accelerates, decelerates and cruises at various speeds. The emissions are collected at the tailpipe and analyzed by a computer to computer the total amount of pollutants in grams per mile (gpm) that are being emitted. The test measures carbon monoxide (CO), unburned hydrocarbons (HC) and oxides of nitrogen (NOX). The I/M 240 test also includes a check of the vehicle's evaporative emissions control system to make sure that the fuel system is not leaking fuel vapors into the atmosphere, and a flow test of the vehicle's canister purge control valve.