California has the strictest emissions program in the country. Smog Check is required for most gasoline vehicles older than 8 model years, every other year at registration renewal, and any time the car changes ownership.
Rules change. Verify the current California requirements with the state DMV or environmental agency before you go. This guide reflects the program as of 2026.
| Item | What the Inspector Checks |
|---|---|
| Visual inspection | Catalytic converter, EGR, EVAP system, fuel cap, PCV, air injection - everything must be factory or CARB-approved. |
| Functional check | Fuel cap pressure test, ignition timing on pre-OBD-II cars. |
| OBD-II scan | 1996 and newer gas cars: MIL command status, codes, readiness monitors. Diesel 1998+ also OBD-II tested. |
| Tailpipe (older cars) | Pre-2000 gas vehicles get an ASM dyno tailpipe test for HC, CO, and NOx. |
| MIL bulb check | Check engine light must illuminate when key is ON and engine OFF - and go off when running. |
| Visible smoke | No visible smoke from exhaust or crankcase. Diesel smoke opacity tested separately. |
Check engine light on (MIL commanded) is one of the top reasons cars fail in this state.
Get a Full Diagnosis →Readiness monitors not ready is one of the top reasons cars fail in this state.
Get a Full Diagnosis →Failed catalytic converter (P0420/P0430) is one of the top reasons cars fail in this state.
Get a Full Diagnosis →EVAP leak / bad gas cap is one of the top reasons cars fail in this state.
Get a Full Diagnosis →Aftermarket / missing CARB EO part is one of the top reasons cars fail in this state.
Get a Full Diagnosis →Visible smoke or oil burning is one of the top reasons cars fail in this state.
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Every two years at registration renewal for gas vehicles 1976 and newer, plus on every change of ownership. Cars 8 model years old or newer are exempt at renewal but still must smog at sale.
Between $30 and $90 depending on the station. STAR stations may charge a bit more. The $8.25 certificate fee is separate. Pay at the station, not the DMV.
STAR stations are higher-performing smog shops. The DMV directs roughly 20% of vehicles (called "directed" vehicles) to STAR stations based on a risk model. Your registration renewal notice tells you if you must use STAR.
You have to repair and retest. California offers the Consumer Assistance Program (CAP) repair assistance of up to $1,200 for income-eligible drivers whose car fails.
Battery-only EVs are exempt. Hybrids must smog like gas cars once they exceed 8 model years, including a full visual and OBD-II inspection.
A passing Smog Check is valid for 90 days. If your registration is not renewed within 90 days you have to smog again.