Smog Check Rules

To help reduce the smog problem created by exhaust from vehicles, states across the country require smog checks of cars and trucks. Usually states only require vehicles in highly populated and polluted counties to undergo inspection. These smog inspections usually take place when you first register the car with the state, then once every two years after that. (See Reference 3.)

Qualifying Vehicles

• Each state will have different rules for which vehicles need to undergo testing, but most states use a time frame in which the car was manufactured. In California, if you register a passenger vehicle or truck manufactured in 1976 or later that is powered by gasoline, propane, natural gas, diesel, or methanol-ethanol fuels, it must pass a smog check of its emission system. (See Reference 3.) Washington requires a smog check of vehicles between five and twenty-five years old. (See Reference 4.) If you register your gas or diesel-powered vehicle in certain counties of Nevada and it has a 1968 or younger model year, you must have it inspected. (See Reference 5.) Most states also require a smog check each time a vehicle is bought or sold unless you present a valid certificate during the title transfer at the Department of Motor Vehicles.

Visual Inspection

• When you take your vehicle in for smog inspection, it will likely undergo a pass or fail visual inspection by a trained technician. The technician will look to see if your emission control system has been installed correctly. This includes the crankcase emission control, thermostatic air cleaner, fuel evaporative system, exhaust gas recirculation, ignition spark controls, fuel-metering system, and air-injection system. If the technician finds that any part of the emission-control system has been tampered with, such as missing part, or is defective, the car will automatically fail inspection. (See Reference 2.)

Emission Control Functional Test

• Your car will also likely undergo a pass or fail emission-control functional test. The technician will use specialized software called the Emission Inspection System (EIS) to complete this test. EIS accesses your car's system through the Diagnostic Link Connector (DLC) located on the dashboard between the driver's side and the middle of the passenger side. This software tests the emission system's capability to communicate, the promptness of system monitors, diagnostic trouble codes and the Malfunction Indicator Light (MIL) command status. (See Reference 2.)

Exemption

• Not all vehicles must go through smog-check inspections. Each state will have its own regulations. If you own a Hybrid, a gasoline-powered vehicle with a 1968 model year or older, a motorcycle, trailer or electric car, you probably do not need to take your vehicle in for inspection. In California, vehicles that operate on diesel and were manufactured before 1998 or that have a Gross Vehicle Weight rating (GVWR) of more than 14,000 pounds do not have to be inspected. (See Reference 1.) Be sure to check with your local DMV for exemptions.

Failure of Smog Check

• If your vehicle fails its smog check, you must have it repaired so it meets your state's emission standards and have it tested again. Some states will allow you to waive the smog check if your car fails the test a second time after repairs. In Washington, for example, if you spend more than $150 on repairs performed by a specialist and your vehicle still fails its smog inspection, the state will allow you to waive the test and still register your vehicle. (See Reference 4.)