Smog Check Tips — How to pass your test

01 — Change the engine oil (only if it needs it)

Dirty oil in the crankcase can release extra pollutants and cause a fail. While the mechanic is changing the oil, ask for a quick visual inspection — cracked, broken, or disconnected hoses can also trigger emission issues.

02 — Make sure the tires are properly inflated

The smog test puts your tires on rollers (a dynamometer) so the engine can run at highway speed while the car stays still. Under-inflated tires make the engine work harder to hit test RPM — and harder-working engines emit more.

03 — Drive at highway speeds for two weeks before the test

Highway driving brings your catalytic converter up to its optimal operating temperature. That sustained heat burns off oil residue, carbon deposits, and fuel byproducts that build up from short city trips and low-speed driving. A clean cat is a huge factor in passing — even two or three 20–30 minute freeway runs in the weeks before the test can move the needle.

04 — Take care of required maintenance early

Handle any required maintenance well before your smog test. Most shops disconnect the battery during a tune-up, which resets the car’s onboard computer — and the OBD system then needs about two weeks of normal driving to run all the diagnostic readiness monitors needed to pass.

05 — Ask about a pre-inspection

A pre-inspection can tell you whether your car is likely to pass before the result gets reported to the state. If you’re worried about a failure on record, ask us — we’ll let you know where you stand.

06 — Check coolant and gas levels before the test

The test runs the engine at high speed while the car stays stationary, so less air flows through the radiator — make sure your coolant is topped off. Also keep the gas tank reasonably full: on a dynamometer, the car may sit at an angle, and a low tank can expose the fuel pump and put vapor in the fuel line, causing a fail.