The three parts of a smog inspection
A California smog check has up to three parts. Which ones apply depends mostly on your vehicle’s model year and fuel type.
1. Visual inspection
The technician confirms that the emissions-control parts that belong on your vehicle are present, connected and have not been tampered with. Missing, removed or modified parts can cause a failure.
2. Functional checks
The technician checks that the emissions-related systems work. The most familiar one is the check engine light, which should come on when you start the ignition and go off once the engine runs. On some vehicles there are additional functional tests.
3. The emissions test
- Computer scan (OBD-II): on most 2000-and-newer gasoline vehicles, the test reads your onboard computer for trouble codes and readiness status, instead of measuring the tailpipe.
- Tailpipe test: older gasoline vehicles, generally 1999 and earlier, get a tailpipe emissions test.
What about diesels?
Diesel vehicles from 1998 and newer that require a smog check get a visual inspection and an OBD-II check, along with a visual check for smoke. There is no tailpipe emissions test for diesels. See our diesel smog check page.
What a smog check does not cover
A smog check is not a safety inspection. It does not check your brakes, tires, lights or suspension, and it is not a general engine tune-up. It looks at emissions equipment only.
How to be ready
- Make sure the check engine light is off.
- Drive about 15 minutes so the engine is warm.
- Avoid battery disconnects or code resets right before testing. See readiness monitors.
- Bring your registration or DMV renewal notice.
For quick answers on requirements, exemptions and fees, visit our California smog check guide.
Sources: the California Bureau of Automotive Repair and the DMV smog check pages. Rules and fees can change, so always check your DMV renewal notice for what applies to your vehicle. This article is general information, not legal advice.
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Read articleNeed a smog check? Just drive in.
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