A California smog check is the emissions inspection most gasoline-powered vehicles have to pass before the DMV will renew their registration, and the Bureau of Automotive Repair runs the program.1Bureau of Automotive Repair. Smog Check: When You Need One and What’s Required The test is required every two years once a gasoline vehicle is more than eight model years old, and separate rules apply when you sell a car, buy one from out of state, or fail an inspection.
When a Smog Check Is Required
Three situations trigger the test. The most common is registration renewal. Your DMV renewal notice will say either “Smog Certification Required” or “Smog Certification Required at a STAR station.” Because the test is biennial, it won’t appear on every renewal.1Bureau of Automotive Repair. Smog Check: When You Need One and What’s Required
The second is a private-party sale. The seller is responsible for the inspection, and the resulting certificate is valid for 90 days. If you’re buying from a private party, confirm the smog check falls inside that window. Vehicles four model years old or newer skip the test on a change of ownership, but the buyer owes the DMV a smog transfer fee instead.1Bureau of Automotive Repair. Smog Check: When You Need One and What’s Required
The third is initial registration in California. Any vehicle previously registered in another state has to pass a California smog check before it can be registered here, which also confirms any aftermarket parts comply with state rules.1Bureau of Automotive Repair. Smog Check: When You Need One and What’s Required
Which Vehicles Are Exempt
Exemptions are broader than most drivers assume, and they vary by fuel type and age.
- Gasoline vehicles eight model years old or newer are exempt from biennial renewal smog checks. Add eight to the model year to see when the first test is due: a 2020 model first needs one for its 2028 renewal.1Bureau of Automotive Repair. Smog Check: When You Need One and What’s Required
- Gasoline vehicles from 1975 or older are permanently exempt.2California Department of Motor Vehicles. Smog Inspections
- Electric vehicles are fully exempt because they produce no tailpipe emissions.2California Department of Motor Vehicles. Smog Inspections
- Diesel vehicles from 1997 or older, or any diesel over 14,000 pounds, are exempt.2California Department of Motor Vehicles. Smog Inspections
- Motorcycles are exempt because the state has not implemented test procedures for them.3California Legislative Information. California Health and Safety Code 44011
- Gasoline-electric hybrids are not exempt. They follow the same rules as gasoline vehicles.
Even an exempt vehicle can be pulled in for testing if the state has reason to believe its emissions system has been tampered with, or if it’s flagged by roadway remote sensing.3California Legislative Information. California Health and Safety Code 44011
Where to Get the Test Done
Not every licensed station can handle every vehicle. Areas that meet federal air quality standards use a basic inspection; areas that fall short use an enhanced inspection, which often involves a dynamometer that measures emissions under simulated driving load rather than at idle.4California Legislative Information. California Health and Safety Code 44010
Some vehicles are routed to STAR stations, which meet higher performance and accuracy standards set by the Bureau of Automotive Repair. Your DMV notice will tell you if a STAR station is required. Vehicles identified as gross polluters and those flagged for higher-risk testing have to use STAR facilities regardless of location.5Bureau of Automotive Repair. STAR Certification A standard station cannot perform your test if the notice specifically names STAR, so check before you drive across town.
STAR stations come in two types. Test-and-repair stations can inspect and fix your vehicle. Test-only stations do the inspection but don’t make repairs, which keeps the result independent. The Bureau of Automotive Repair maintains a searchable directory at bar.ca.gov where you can filter by location and service type.6Bureau of Automotive Repair. Auto Shop Locator
How to Prepare
Bring your DMV renewal notice. The barcode on it links your vehicle to the state database so the technician can pull your records. If you’re returning for a retest, bring the earlier Vehicle Inspection Report showing what failed.
Check your dashboard before you leave. An illuminated check engine light is an automatic failure no matter what your tailpipe emissions actually measure, so get it diagnosed and repaired first. Paying for a test you’re guaranteed to fail is wasted money.
Drive the car for at least fifteen minutes beforehand. The catalytic converter needs full operating temperature to process exhaust properly, and a cold engine produces skewed readings that can push an otherwise compliant car into failure range. Sustained highway speed heats the system more efficiently than stop-and-go traffic.
OBD Readiness Monitors
This one catches people off guard. Your car’s onboard computer runs internal self-tests called readiness monitors that check emissions systems. If those monitors haven’t completed, the station will reject the test before it starts. A recent battery disconnect, a battery replacement, or clearing diagnostic trouble codes all reset the monitors to “not ready.”7Bureau of Automotive Repair. New OBD Readiness Monitor Regulations Explained
How many unset monitors you’re allowed depends on your vehicle:
- Gasoline, 1996–1999: one unset monitor allowed.
- Gasoline, 2000 and newer: only the evaporative system monitor may be unset.
- Diesel, 1998–2006: no unset monitors allowed.
- Diesel, 2007 and newer: only the diesel particulate filter and non-methane hydrocarbon catalyst monitors may be unset.7Bureau of Automotive Repair. New OBD Readiness Monitor Regulations Explained
Some monitors set quickly in normal driving. Others need specific conditions, like sustained highway speed or a cold start followed by city driving. After repairs or a battery replacement, plan on driving 50 to 100 miles over several days before scheduling the test. An inexpensive OBD scanner will tell you which monitors are ready.
What the Test Checks
The inspection has three parts, and knowing them explains why a car that runs fine can still fail.
The visual inspection confirms that all factory-installed emissions equipment is present and unmodified, including the catalytic converter, the exhaust gas recirculation valve, and the positive crankcase ventilation system. A missing, disconnected, or non-compliant aftermarket component fails the car even when actual emissions are clean.8Justia. California Health and Safety Code 44012
The functional test checks components like the gas cap with a pressure tester to confirm it seals against fuel vapor leaks. A leaking gas cap is one of the cheapest and most common failure causes. The technician may also check ignition timing where it applies.
The emissions measurement is the main pass/fail step. For 1996 and newer vehicles, the state’s inspection system communicates directly with the car’s onboard diagnostics to download performance data and any stored trouble codes. Older vehicles get a tailpipe test that measures the actual chemical composition of the exhaust while the engine runs, and in enhanced areas the dynamometer measures emissions at different simulated speeds. Results transmit to state servers in real time.
Cost and Results
Most California smog checks run between $30 and $80. Stations in enhanced-testing areas tend to charge more. The station must disclose the certification fee, labor, and any additional charges before starting work.
When your vehicle passes, the technician gives you a Vehicle Inspection Report and sends the result to the DMV electronically. You don’t deliver paperwork yourself; the DMV can issue your renewal tags as soon as the passing result lands in their system.
If Your Vehicle Fails
A failure doesn’t mean you’re stuck. California offers several routes forward, and the right one depends on repair costs and whether the car is worth keeping.
Repair and Retest
The Vehicle Inspection Report identifies what failed. Common culprits are faulty oxygen sensors, a worn catalytic converter, vacuum leaks, and misfiring spark plugs. After repairs at a licensed facility, the car needs a retest. Many stations offer a free retest within 30 days if you return to the shop that performed the original test.
Consumer Assistance Program Repair Help
If your household income is at or below 225% of the federal poverty level, the Bureau of Automotive Repair’s Consumer Assistance Program can help pay for emissions repairs. The ceiling depends on model year:
- 1996 and newer: up to $1,450 in repair assistance, with a 20% co-payment on total diagnostic and repair costs.
- 1976–1995: up to $1,100 in repair assistance, also with a 20% co-payment.9Bureau of Automotive Repair. Apply for Repair Assistance
Repairs have to be done at a STAR test-and-repair station to qualify. Anything above the assistance maximum comes out of pocket.
Repair Cost Waiver
If you’ve spent at least $650 on emissions-related repairs and the car still can’t pass, you may qualify for a one-time repair cost waiver that lets you register it anyway. The requirements are strict: the vehicle has to be in its biennial renewal cycle, the $650 must be spent at a licensed test-and-repair station on qualifying diagnostics and emissions repairs, and the car has to fail the retest after those repairs. Vehicles with tampered, missing, or disconnected emissions equipment don’t qualify. The waiver is limited to one per vehicle per registered owner and doesn’t apply to change-of-ownership or initial registration inspections.
Vehicle Retirement
For older cars where repairs cost more than the vehicle is worth, California will pay you to take it off the road permanently. The incentive depends on income and the car’s recent inspection history:
- $1,350 regardless of income if the vehicle failed its most recent smog check.
- $1,500 for income-eligible owners (at or below 225% of the federal poverty level) whose vehicle has a completed smog check within the past 180 days, whether it passed or failed.
- $2,000 for income-eligible owners whose vehicle failed its most recent smog check.10Bureau of Automotive Repair. Retire Your Vehicle
The car has to be drivable under its own power to a BAR-contracted dismantler, with all major body components intact. Vehicles that failed solely because of a tampered emissions system, a bad gas cap, or an ignition timing issue don’t qualify for the retirement incentive.10Bureau of Automotive Repair. Retire Your Vehicle
Tampering Disqualifies You
Removing or modifying emissions controls is illegal under California and federal law. A vehicle with tampered equipment automatically fails a smog check and is disqualified from both the repair cost waiver and the retirement incentive. The car stays unregistrable until the original equipment is restored and it passes a clean test.