California Smog Check - AAA DMV services (2024)

Vehicle emissions are a significant source of smog in California, which is why the state adopted its Smog Check Program in 1984.

The program identifies and requires repairs for vehicles that emit excess smog-producing pollution. Smog checks take place when vehicle owners renew their registration or transfer their vehicle to someone other than a family member. Not every vehicle needs smog checks, though, and the technical details of smog checking have changed significantly over time.

Which cars need smog checks

Gasoline, hybrid, light natural gas, and flex-fuel vehicles, model year 1976 or later

• A smog check is required every other year, unless the vehicle is 6 or fewer model years old.
• A smog check is also required to transfer ownership, unless the vehicle is 4 or fewer model years old.

Diesel passenger cars and light trucks, model 1998 or later

• A smog check is required every other year or when ownership is transferred.

Most other vehicles are exempt from smog inspections

• That includes gas vehicles model year 1975 or older, diesel vehicles model 1997 or older, electric vehicles, and motorcycles.

What a smog check involves

Originally, smog checks included tailpipe, visual, and functional inspections. Today, most gasoline vehicles model year 2000 or newer and diesel vehicles model 1998 or newer no longer require a tailpipe inspection, where exhaust is analyzed while the vehicle is driven on a stationary dynamometer. That’s because modern cars are cleaner and have sophisticated onboard diagnostic systems that monitor and identify emission-control problems.

Rather than analyzing exhaust for excess emissions, technicians can connect directly to a modern car’s onboard diagnostics. If there is a problem with a vehicle’s emissions, a technician can read the assessment and quickly get an idea of what repairs might be required.

How to know if your readiness monitors haven't finished

The Check Engine light will come on if your vehicle's readiness monitors find a problem, but there's no dashboard indicator if they've completed successfully. In many newer vehicles, if the driver turns the ignition key to the “on” position without starting the car (the “accessory” position), the Check Engine light should stay on. If it flashes after 15 seconds, the readiness monitors aren’t complete.

How to help your vehicle complete its readiness monitors

Smog check stations can provide guidance on the type of driving needed for a vehicle to complete its readiness monitors after a repair or memory wipe. In general, you'll want to follow these steps:

• Drive at steady speeds
• Avoid hard acceleration
• Keep the gas between a quarter and three-quarters full
• Drive at least 50 miles, both city and highway

Readiness monitors mean you can't hide fault codes

Fault codes can’t be hidden by erasing them or disconnecting the battery; the readiness monitors must be completed to determine if the fault still exists, or the vehicle won't pass a smog check.

If a vehicle’s readiness monitors continually won’t complete, it may mean that the vehicle has a malfunctioning component or sensor that needs to be adjusted or replaced.