Smog Check Tips — how to pass your test in Glendale
A few simple steps before your inspection make a huge difference — especially on older cars. Here’s how to set yourself up to pass on the first try.
Ready when you are — our hours and directions →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.
What actually fails a car
Most of the cars that do not pass are not broken in any dramatic way. They turn up with one of these four things, and three of them are fixable before you ever drive over here.
The check engine light is on
This is an automatic fail on an OBD-II vehicle, no matter how clean the tailpipe is. If the light is on, get the code read and the fault fixed first — bringing it in lit is a wasted trip.
The readiness monitors have not set
Disconnect the battery or clear a code and the car's self-tests reset. Until it has driven enough normal miles to run them again, it cannot be certified. This is the single most common reason a perfectly healthy car gets turned away.
A cold or short-tripped engine
A catalytic converter only does its job hot. A car that lives on five-minute errands never gets there, and its numbers show it. Twenty minutes of freeway on the way over is genuinely worth doing.
Something visible is missing or modified
The inspection includes a visual check. A missing gas cap, a disconnected hose, a removed or non-compliant part will stop a car that would otherwise sail through the tailpipe test.
If your car does fail here, the re-test after repairs is free. Ask us about a pre-inspection first if you would rather know where you stand before a result goes on record.
Can’t afford the repairs? California’s Consumer Assistance Program may cover them →