Overview of In-Use Compliance Testing
Exhaust Testing
Selected vehicles are placed onto dynamometers, or more specifically a chassis dynamometer used to produce resistance for the engine. As the engine works to spin the wheels, the emissions emitting from the tailpipe are analyzed. This type of testing is identical to a vehicle’s certification testing.
Portable Emissions Measurement System (PEMS)
PEMS is a self-contained portable emissions measurement system that provides a detailed emissions analysis, similar to the certification testing results. PEMS testing is done in “real-time” as the vehicle is driven, which is in strong contrast to certification testing which requires an emissions laboratory for testing.
Sealed Housing Evaporative Determination (SHED) Testing and On-board Refueling Vapor Recovery (ORVR)
Sealed Housing Evaporative Determination(SHED) and ORVR testing simulate the two scenarios where a vehicle is parked or refueling and checks for evaporative emissions. Vapors from a parked vehicle's fuel tank while collected in a canister can escape in small amounts. Rubber, plastics, and other materials on the vehicle may also contribute to emissions. In an ORVR chamber, the vehicle is connected to a nozzle similar to those at gas stations and pumped to fill up the fuel tank while the air is monitored to check for escaping vapors.
On-Board Diagnostic (OBD)
OBD is the name of the computerized system beginning with MY1996 and newer vehicles that have a GVWR under 14,000 pounds, to monitor the vehicle's emission control system performance and notify the driver, by illumination of the “Check Engine Light,” when defects that cause an increase in air pollution are identified.
Auxiliary Emission Control Device (AECD)
AECD means any device or element of design that senses temperature, vehicle speed, engine revolutions per minute (RPM), transmission gear, manifold vacuum, or any other parameter for the purpose of activating, modulating, delaying, or deactivating the operation of the emission control system.