Everything California drivers need to know about SMOG checks.
Plain-English guides covering rules, exemptions, STAR stations, failed-test options, and how to prepare your vehicle.
What do you need to know?
What is a SMOG check?
California's emissions inspection program, explained
Who needs one?
Find out if your vehicle requires an inspection
How to pass
6-step checklist for your appointment
Failed your test?
Next steps, repairs, and assistance programs
STAR stations
When STAR is required and what it means
Repair assistance
How the CAP program helps with costs
SMOG glossary
BAR, CAP, OBD-II and other terms decoded
East Bay SMOG rules
Inspection rules for Contra Costa County drivers
Common SMOG questions, answered
Tap any question to expand. More detailed guides are linked in each answer.
Prices vary by station and vehicle age. Most stations charge between $30 and $80 for the inspection itself, plus an $8.25 state certificate fee. STAR stations may charge more because they handle stricter requirements. In Concord, Super Station offers $49.75 for 2000 and newer gasoline vehicles.
Most gasoline vehicles in California need a SMOG inspection every other year (biennially) for registration renewal. Your DMV renewal notice will tell you exactly when yours is due and whether a STAR-certified station is required.
The biggest cause is a check engine light that's on — that's an automatic failure. Other common reasons: incomplete readiness monitors, a failing catalytic converter, EVAP leaks (often from a bad gas cap), or visible modifications to emissions components.
Technically yes, but it usually makes things worse. Clearing codes resets your readiness monitors, and the vehicle needs 50-100 miles of driving to complete them again. Without completed monitors, the SMOG station cannot finish your test.
Don't panic. You'll get an inspection report showing exactly what failed. Fix the underlying issue, then return for a retest. If repair costs are high, you may qualify for the California Consumer Assistance Program (CAP).
Recent SMOG updates & tips
New article every Tuesday. Swipe to browse.
How Often to Check Your OBD2 Readiness Monitors
Learn how often to check your OBD2 readiness monitors before a California SMOG test and why unset monitors cause an automatic failure.
Read article → California SMOG RulesDiesel SMOG Check Requirements in California
Does your diesel vehicle need a California SMOG check? Learn which diesels are tested, what inspectors look for, and how to pass.
Read article → SMOG Check TipsHow to Read OBD-II Codes Before Your SMOG Test
Learn how to read your car's OBD-II codes before a California SMOG check and avoid a costly failed inspection. Practical steps explained.
Read article →Book your SMOG check with Super Station Concord
This site is the educational resource of Super Station Concord — a STAR-certified test-and-repair station serving Concord, Walnut Creek, Pleasant Hill, and the rest of the East Bay. Use the coupon below for your next inspection.
Still have questions?
Browse the full library of California SMOG guides. Every article is free, updated regularly, and sourced from BAR and DMV.