Smog check tips

Give your car its best shot at passing.

A few simple things before your visit can be the difference between a pass and a return trip. Here’s what actually helps — from a Modesto station that tests thousands of cars a year.

(209) 577-1644 Get directions

Before you come in

Six tips that help you pass.

None of these cost anything, and together they give an otherwise-healthy vehicle its best chance of passing the first time.

Drive it 15 minutes first

A warm engine and a hot catalytic converter burn far cleaner. A cold start can fail a test the same car would pass once it’s up to temperature.

Fix the check-engine light

An illuminated check-engine light is an automatic fail on any OBD-II vehicle, no matter how clean it runs. Have the code read and repaired first.

Don’t clear codes right before

Clearing codes or disconnecting the battery resets the readiness monitors, which fails the test until they complete — often several days of normal driving.

Keep up basic maintenance

Regular oil changes and tune-ups per your owner’s manual — and never tampering with emissions equipment — are the surest path to clean numbers.

Check tire pressure & gas cap

A loose or cracked gas cap can trip an evaporative code, and correct tire pressure helps on the dynamometer for older vehicles.

Bring your renewal notice

It tells us exactly what the DMV is asking for, so we can run the right test the first time.

If you still don’t pass

You have options.

The single biggest cause of avoidable failures we see is readiness: a car that was recently jump-started, had its battery replaced, or had codes cleared simply hasn’t finished its self-checks yet. If any of that happened recently, drive normally for a few days before coming in.

And if your vehicle does fail, don’t worry — we’ll explain exactly what to repair, and you may qualify for up to $500 in repair help through the state’s Consumer Assistance Program. See the details on our resources page. Se habla español.

Tips FAQ

Pass-your-smog questions.

Will a warm-up really help?

Yes. Emissions equipment works best at operating temperature, so a 15-minute drive beforehand gives you the best shot.

My check-engine light is on — should I still come?

If the light is on, an OBD-II vehicle will fail. Best to have the light diagnosed and repaired first, then come in.

Should I clear the codes before my test?

No. Clearing codes resets the readiness monitors, which fails the test until they run again. Just repair the issue and drive normally.

How do I know my car is ready to test?

Drive it normally for several days after any battery disconnect or repair so the readiness monitors complete before you come in.

Does a loose gas cap matter?

It can. A loose or cracked gas cap trips an evaporative fault — tighten or replace it before your visit.

What if I fail?

We’ll explain why and what to fix, then retest you after the repair. You may also qualify for help through the Consumer Assistance Program.

Do I need an appointment?

No — walk in Monday through Friday. Hours are in the header and footer.

$49.75 smog check in Modesto. Se habla español.

1324 N CARPENTER RD · STAR STATION · TEST-ONLY

(209) 577-1644