What happens if your car fails a smog check

A failed smog or emissions test is not a moving violation, and the station does not impound your car. You should receive a Vehicle Inspection Report showing why it failed. Keep it. A mechanic needs those results before giving you a useful diagnosis or estimate.

The station usually reports the result to the state. Trying another shop will not erase it. In most cases, the immediate problem is registration: you will need a passing result or a qualifying exemption before you can renew.

• OBD-II failure. The computer has a stored trouble code, the check engine light is on, or too many readiness monitors show "not ready." That last one is common after the battery has been disconnected or codes have been cleared.
• Tailpipe failure. Hydrocarbons, carbon monoxide, or NOx exceed the limit for your vehicle's year and weight. Common causes include a worn catalytic converter, a bad oxygen sensor, a fuel-control problem, or engine wear.
• Visual failure. An inspector sees missing or altered equipment: a removed cat, a deleted EGR or air pump, a straight-piped exhaust, an uncertified intake, or a tune that is not approved for road use. Restoring that equipment can get expensive quickly.

• Loose or cracked gas cap: under $30.
• Drive cycle to set readiness monitors: free, just time.
• Oxygen sensor: roughly $150–$450 installed.
• EVAP purge valve or vacuum leak: $150–$500.
• Catalytic converter: $800 to well over $3,000 on modern and European cars. A new converter can fail again if the problem that damaged the old one is not repaired.
• Restoring deleted emissions equipment on a diesel or modified gas engine: frequently thousands of dollars, and sometimes more than the vehicle is worth locally.

Before deciding, compare a written repair estimate with the car's value after it passes. A $200 repair on a dependable daily driver is an easy call. A $3,000 converter on a $4,000 car deserves a closer look.

Some states offer a repair-cost waiver. You spend a required amount on qualifying repairs at an approved shop, return for a retest, and may receive a temporary waiver if the car still fails. California, Colorado, and several other states also offer repair assistance for owners who meet income requirements.

Check for age and use exemptions as well. Some states exempt older model years or vehicles with collector registration. Others test only in certain metro areas. Two people in the same state can face different requirements because they live in different counties.

These programs change. Confirm the current rules with your DMV or state emissions program before spending money or selling the car.

Fix a small, certain problem. Think twice about a large repair that will not add the same amount back to the car's value.

Local buyers will usually subtract the full repair estimate, plus a little extra for risk. A buyer in an area without emissions testing may look at the car differently. So might someone shopping for a track car, farm truck, off-road build, or parts donor.

Unsmoggables is built for those buyers and sellers. You can list a modified, deleted, swapped, or non-passing vehicle without burying the issue in the description. Be specific about what failed and include the inspection report when possible.

Put the failed test in writing, keep a copy of the report, and check the seller requirements in your state. An "as-is" bill of sale does not cancel a law that requires the seller to provide a passing certificate.

• How to sell a car that fails emissions — the full step-by-step: pricing, disclosure, and listing.
• Emissions testing by state — see which states and counties don't test at all.

Plenty of people go looking for these cars on purpose. If the failure is a sensor or an unset monitor, the discount is often bigger than the repair. If you live where there's no testing, or the car is headed for a track, farm, or build, the failure costs you nothing at all.

Ask for the inspection report before you talk price, and check the rules in the county where you'd register it rather than where the car is sold.

• What to check before buying a car that failed emissions — codes, costs, registration and inspection.
• Browse cars listed as non-passing — the failure is stated up front.

Can I still drive my car if it fails a smog check?

Usually, yes, as long as the registration is still current. The failed test normally prevents you from renewing it. Once the tags expire, driving the car can lead to a citation. Check your state's rules and the date on your registration.

How long do I have to fix it?

Start with your registration deadline. That usually matters more than the day the car failed. Many stations include a free or discounted retest within 30 to 90 days, so ask about the deadline before you leave.

What does it cost to pass?

It could be nothing more than a loose gas cap or an incomplete drive cycle. An oxygen sensor usually costs a few hundred dollars. A catalytic converter on a modern car can run $1,500 to $3,000 or more, so get a diagnosis before approving repairs.

Can I sell a car that failed smog?

Often, but the rules depend on the state. Some states make the seller provide a passing certificate. Others allow an as-is sale with written disclosure. Out-of-state sales may also be possible. Disclose the failure in writing and confirm the rules where the car is being sold.