Why SMOG Check

Smog Check Process in California

In an effort by the state to improve the quality of air intake, Vehicles in California undergo a mandatory smog check every two years at locations approved by DMV (Department of Motor Vehicles) in every county to identify and repair those with excess emissions. This is a pre-requisite required for vehicle registration and renewal after an initial inspection for both new and old residents whether or not they have been certified from their previous states. The smog check process is administered by the Bureau of Automotive Repair (BAR) in the California Department of Consumer affairs through over 7000 state-licenced and private stations) and has indeed greatly reduced air pollution emitted from millions of cars in California.

New residents are allowed 20 days after their residency has been granted to carry out a smog check. They must present a smog check certificate before their vehicles are registered. First the DMV demands for the Vehicle Identification Number, with which one may look up a vehicle test history. Smog certification is valid for 90 days upon inspection for old residents, within this period they must register their vehicle or renew their registration. On completion of initial smog check, re-certification is mandated every 2 years and the time due for next smog check is indicated on the registration or renewal reminder. A Vehicle Inspection Report (VIR) is given at the smog stations on to indicate a pass or failure after completing the smog test. A failure code during emission check will result to a failure in a vehicle’s smog inspection. A vehicle required by the state to be checked for smog is called a Directed vehicle. Smog checks are performed at stations called STAR certified stations which must meet the standards certified by the Bureau of Automotive Repair (BAR).

3 checking process

The California smog checking process consists of three basic processes in the order listed below. A vehicle must pass all the three test processes to pass the California smog check.

  1. Emissions check: This is performed on 1999 and older vehicles by the exhaust gas analyser also known as the smog machine. It checks for the presence of Carbon Monoxides, Hydrocarbons, and Nitrogen Oxides in the vehicle’s exhaust which is known to produce smog.
  2. The Visual check: This check is most suitable for 2000 model year and newer vehicles. These vehicles are administered a visual smog check and OBD test, omitting the tailpipe test as part of the new DAD IOS test system.
  3. The Functional check: Also a part of the new DAD IOS smog test, a functional checked is administered for OBD II trouble codes and readiness monitors by a smog technician or smog machine.

Enhanced Smog Test

The processes listed above is the Basic Smog Check required for counties in California with a low smog pollution, this test is done at idle and 2500 rpms. However, a process proven to be more accurate in checking vehicle emissions called the Enhanced Smog Test is required in counties recorded to have higher smog pollution. In this process, the smog machine collects emissions from the exhaust as the vehicle is driven on a Dynamometer.

Change of Ownership areas

There are counties with lesser air pollution. In these counties called ‘Change of Ownership’ areas, vehicles required to undergo smog test are those imported into California with the exception of those produced according to California certification.


Smog Check Requirements

  • A smog check is required every two years upon renewing the registration of hybrid, gas-powered, and flex-fuel vehicles of model year 1976 or later models.
  • Same is applicable for diesel-powered vehicles of model year 1998 or later with a weight rate of 14,000 pounds or more.


The following categories of vehicles are exempted from the biennial smog check:

  • Newer vehicles such as six model-year or later models with the exception of diesel-powered vehicles are considered to be cleaner and unlikely to fail a smog check.
  • Much newer vehicles such as four model-years old vehicles has no need to be smog checked even when a change of ownership occurs
  • 2000 model year and newer vehicles
  • Gasoline-powered vehicles model year 1975 and older
  • Natural gas-powered vehicles weighing over 14,000 lbs
  • Model year 1997 and older Diesel-powered vehicles
  • Electric vehicles
  • Motorcycles
  • Counties such as El Dorado, Placer, Sonoma, Riverside and San Diego require smog check in certain zip codes only. Simply enter a zip code to determine if vehicles in these counties require smog check.
  • Abatement fee: Vehicles that are 6 years old or less do not require biennial smog check, owners are rather required to pay $20 annually up to 6 years of registration for smog abatement fee. Smog check is administered after these 6 years. However, non-resident vehicles, model year 1998 Diesel-powered vehicles and newer weighing less than 14,000 lbs, model year 1976 and newer are part of the smog check program.

Referee Program

Inspection centres are positioned across the states to assist vehicle owners solve issues related to smog checks which are not available at the stations. Referees resolve issues such as:

  • Smog check dispute
  • Repair cost waivers
  • Vehicle’s OBD II System
  • Refusal of smog check stations to assist consumers
  • Gross polluter vehicles
  • Specially constructed vehicles
  • Law enforcement citations for various cases
  • Smog check exempt vehicles
  • Grey market and change engine vehicles

New Smog Check Technology

A new technology was legislated in 2010 (AB 2289-Eng) to improve on the traditional smog check program. It is a computer-based smog test which uses the diagnostics capabilities of a vehicle’s computer system to determine vehicle’s emission instead of the long existing tailpipe test. It uses information gathered from the On-Board Diagnostic (OBD) system to check if a vehicle’s emission system is working properly. This new technology performed alongside a visual inspection of emission control components is applicable to most diesel-powered vehicles model-year 1998 and newer, gasoline cars that are model-year 2000 and newer as well as hybrid vehicles. In addition, most 1996 and newer vehicles with a gross vehicle weight rating less than 14,000 pounds have in-built second-generation OBD systems (OBD II). Another important advantage of OBD II is that it monitors the emission control system of a vehicle and alerts the driver of any defect arising from increased a pollution.

Types of Smog Stations

STAR Stations

Test-Only Stations

Test-and-Repair Stations

Repair-Only Stations

STAR Stations are smog check stations that meet the specified performance standard established by BAR. Directed vehicles and gross polluters must receive certification from a STAR-certified station as often recommended by BAR or as indicated on the registration renewal issued by the Department of Motor Vehicles. While some star stations are licenced to perform tests and repairs (Test-and-Repair Stations), some are licenced to perform only tests (Test-Only Stations), and others only repairs (Repair-Only Stations). A vehicle can be checked for smog at any smog station unless it is required to a check at a STAR station.

At the Smog station

Before a vehicle is checked for smog at a station, a Registration Renewal Notice from the DMV and a payment method must be presented.

To identify a vehicle, an Inspector first input the Vehicle Identification Number (VIN) and/or Licence plate number following the (Emissions Inspector System) EIS or OIS prompts to verify that the VIN shown on the registration document matches the VIN on the vehicle. It is prohibited to enter any VIN for any vehicle other than the one being tested.

In performing a Smog Check, a device connected to computers at BAR is connected to the vehicle by a licenced inspector. If the test is successful, a test result called Vehicle Inspection Report (VIR) is issued to the vehicle owner and also transferred electronically to the DMV.

If the test was conducted for the purpose of renewing a registration, this can be proceeded at the DMV. However, if a vehicle fails a smog test, the following actions can be taken by the vehicle owner:

  • Diagnosis and repair at a licenced repair facility. Vehicles must be re-tested after undergoing repair. Those tested at a STAR station must be re-tested there.
  • Get the opinion of a referee if unsatisfied with the test results.
  • Seek financial aid from Consumer Assistance Program (CAP) if eligibility requirements are met. CAP can also assist in Vehicle retirement if vehicle is beyond repair.
  • Utilise the Referee Network for a Repair Cost Waiver if unable to pay for repair.