Glossary of Terms Used By Auto Smog Testing & Repair Shops

Educate yourself on smog check industry terms and processes.

This glossary includes terms and definitions that will help demystify the vehicle emissions testing process.


California Air Resources Board
The agency that oversees air quality in the state of California. Also known as the Air Resources Board, the CARB writes and enforces the rules and regulations for air quality standards.

Also known as: Air Resources Board, ARB, CARB


average emissions
The number of average emissions that serve as a guide for auto smog repair technicians when a vehicle fails its smog check. Average emissions are set based on the model, year and type of vehicle (passenger car, light truck, medium truck, heavy duty truck, etc.).

Also known as: AVE


Bureau of Automotive Repair
California’s consumer protection agency for vehicle owners. The Bureau of Automotive Repair (BAR) licenses and oversees auto repair dealers, smog check stations and smog check inspectors. It also investigates consumer complaints about smog check stations, vehicle emissions testing centers, and other automotive repair and maintenance issues.

Also known as: BAR


carbon dioxide
An odorless, colorless greenhouse gas that’s generated by gasoline- and diesel-powered engines. Carbon dioxide is one of the pollutants that auto smog testing looks for.

Also known as: CO2


carbon monoxide

A colorless, odorless gas that can be fatal in moderate and high concentrations. Carbon monoxide emissions occur when fuel is too rich. Large amounts of carbon monoxide emissions can cause a vehicle to fail its smog test.

Also known as: CO


catalytic converter

An auto part above the muffler that turns hydrocarbons, carbon monoxide, oxygen, and nitrogen oxide into carbon dioxide and water vapor for use by the vehicle.

Also known as: CAT


Consumer Assistance Program
A program that helps consumers whose vehicles have failed their vehicle smog test. The Consumer Assistance Program (CAP) can provide up to $500 in auto emissions system repairs, and $1,000 to $1,500 to consumers who would rather retire a failing vehicle than repair it.

Also known as: CAP


directed vehicles

Cars and trucks that must visit a test-only station or STAR emissions testing station. These vehicles usually have a history of failing smog tests, are a make or model known to fail, or have been chosen by random selection for test-only emissions certification.

Also known as: test-only vehicles, DMV test only directed vehicles


Department of Motor Vehicles

California’s licensing agency for vehicles. The DMV is also the agency that requires vehicles to be smog certified and directs certain vehicles to test-only stations.

Also known as: DMV


emission standards category
The pass and fail emission level points for vehicles. Vehicles manufactured from 1976 to 1995 have different ESCs based on their model, make, type, weight, and transmission and engine size.

Also known as: ESC


emissions test

A test that uses an analyzer to test the emissions coming from a vehicle’s tailpipe. Emissions tests and smog tests measure carbon monoxide, carbon dioxide, hydrocarbons, oxygen and nitrogen oxide. Vehicles that fail these emission tests may be labeled gross polluters and are required to be repaired and pass another emissions test to be certified.

Also known as: car smog test, auto emissions test, vehicle emissions test, vehicle smog test


Evaporative Emission Control System
Also known as EVAP, this system prevents raw gasoline from evaporating into the atmosphere. Auto smog testing inspectors often test the EVAP system for defects, modifications and other problems. The EVAP system is part of the smog certification process, and a vehicle can pass or fail based on this part of the test.

Also known as: EVAP, fuel evaporative controls, EVAP system, fuel evaporative system



The gases that are produced when fuel combusts in the engine. Exhaust can also be the term used for the exhaust system of a vehicle, including the catalytic converter, muffler and tailpipe.

Also known as:auto exhaust, car exhaust system, vehicle exhaust system, vehicle exhaust gasses


fuel cap test
Flaws in fuel caps can cause a vehicle to fail emissions testing. Gasoline fumes can leak out around ill-fitting or cracked fuel caps, so smog testing professionals will often perform a visual test to look for any defects, cracks, deterioration, seal problems or other flaws. They will also detect whether any fuel evaporation fumes are coming from the fuel cap area.

Also known as: fuel cap integrity test, fuel cap visual test


functional inspection
This is performed during a smog test and includes checking the mechanical systems of the vehicle, including the EGR, MIL, OBD II, ignition timing, fuel cap and evaporative emissions systems. When these systems leak, they can contribute to unhealthy air quality, so vehicles that fail this functional inspection can fail the overall smog inspection.

Also known as: functional smog inspection, functional systems inspection


gross polluter

Vehicles that fail emissions testing. Typical emissions of gross polluters are usually at least two times higher than a regular failing vehicle. Gross polluting vehicles must be tested and certified by test-only or STAR stations.

Also known as: GP, polluting vehicle, vehicle that failed smog testing


grey market vehicle

Cars and trucks that were manufactured outside of the United States and are not originally designed to meet federal vehicle emissions standards. These vehicles must be modified and tested in order to be legal to drive in California.

Also known as: gray market vehicles


measured emissions
The amount of each pollutant that is measured during a typical auto smog emissions test

Also known as: MEAS


OnBoard Diagnostics II is the second generation of onboard self-diagnostic equipment in vehicles. These onboard diagnostics include “check engine” lights and other warning lights that alert drivers of defects or problems in the emissions system that need to be repaired by a professional.

Also known as: OnBoard Diagnostics II, OBD2, Check Engine light


smog test-only station
A licensed smog check station that is only allowed to test vehicles. They can’t make repairs to vehicles that fail smog inspections.

Also known as: test-only stations, test-only emissions shops, emissions testing only stations


smog test and repair station
A licensed smog check station that can perform smog testing and repairs

Also known as: test & repair stations, smog testing and repairs


STAR program
A state program that certifies certain stations that are more closely monitored by the BAR to perform smog testing and repairs

Also known as: STAR smog stations, STAR test only stations, STAR test and repair stations


smog check certificate
The DMV smog certificate given to vehicles that pass smog testing

Also known as: smog testing certificate, smog certificate, emissions testing pass certificate


smog test coupons
Some smog testing shops offer coupons for emissions testing. While some of these coupons are legitimate ways to save money, some can be a bait-and-switch tactic to get customers in the door. As with every type of business, be wary of deals that seem too good to be true.

Also known as: emissions test coupons, smog coupons


vehicle inspection report
A printout that shows the consumer how their vehicle fared in the vehicle inspection. It also shows the readings, emissions results and station information.

Also known as: VIR