How Long Does a Smog Check Take?
Quick Answer
20–30 minutes at a certified testing station. The actual emissions test runs about 10–15 minutes, with the rest spent on paperwork and visual inspection.
Typical Duration
Quick Answer
A smog check takes 20–30 minutes from start to finish at a certified testing station. The emissions test itself is about 10–15 minutes, and the remaining time covers a visual inspection and paperwork.
What Happens During a Smog Check?
| Step | Time | What the Technician Does |
|---|---|---|
| Check-in and paperwork | 3–5 min | Verify VIN, registration, and mileage |
| Visual inspection | 3–5 min | Inspect exhaust system, gas cap, hoses, and emission components |
| OBD-II scan | 5–10 min | Plug into diagnostic port to read emissions data and trouble codes |
| Tailpipe test (if required) | 5–10 min | Measure exhaust gases while the engine runs |
| Results and certificate | 2–5 min | Print results, issue pass/fail certificate, submit to DMV electronically |
Most modern vehicles (1996 and newer) undergo an OBD-II-based test, which is faster than older tailpipe-only methods.
How Much Does a Smog Check Cost?
Prices vary by state and station:
- California – $30–$90 (average around $50)
- Nevada – $25–$30 at the DMV emission lab
- Arizona – $17 at ADEQ stations
- Colorado – $15–$25
Some stations offer coupons or discounts for returning customers. Star-certified stations in California (required for certain older vehicles) tend to charge on the higher end.
Which States Require Smog Checks?
Not every state mandates emissions testing. States with programs include:
- California – Biennial smog check for most vehicles
- New York – Annual emissions inspection
- Texas – Annual for vehicles in certain counties
- Colorado – Biennial in the Denver metro area
- Arizona – Annual in the Phoenix and Tucson metro areas
- Nevada, Connecticut, Illinois, Ohio, Virginia and others have varying requirements
Check your state's DMV website for specific rules, exemptions, and testing schedules.
Common Reasons for Failing a Smog Check
About 15–20% of vehicles fail on their first attempt. The most common causes are:
- Check engine light is on – An illuminated MIL (malfunction indicator lamp) is an automatic failure in OBD-II testing.
- Catalytic converter issues – A worn or damaged converter cannot reduce emissions to acceptable levels.
- Oxygen sensor failure – Faulty O2 sensors send incorrect data to the engine computer.
- Loose or missing gas cap – A bad seal causes evaporative emission leaks.
- Rich or lean fuel mixture – Dirty fuel injectors or a failing mass airflow sensor can throw readings off.
What to Do If You Fail
- Get the repair estimate – The test station will tell you which components failed.
- Check state assistance programs – California offers the Consumer Assistance Program (CAP), which provides up to $1,200 in repair vouchers for qualifying vehicles.
- Fix the issues and retest – Most states allow a free retest within 30–60 days at the same station.
- Consider a STAR station – In California, vehicles that fail must be retested at a STAR-certified station.
Tips to Pass the First Time
- Drive the car for 15–20 minutes before the test – A warm engine produces cleaner emissions.
- Make sure the check engine light is off – If it is on, diagnose and repair the issue first.
- Top off fluids and replace the air filter – Clean air intake helps combustion efficiency.
- Use a fuel system cleaner a week before your test to reduce carbon deposits.
- Ensure the gas cap seals properly – Replace it if it clicks loosely or the rubber is cracked.
Bottom Line
A smog check takes just 20–30 minutes and is a straightforward process at any certified station. Drive your car warm, make sure the check engine light is off, and you should be in and out quickly.