To pass a smog emission test, the automobile must be in good operating condition and pass the mechanical and visual tests. Autos with the check engine light illuminated automatically fail the test, so operators should have the engine scanned and make the required repairs before going to the inspection.
Operating the vehicle at normal highway speeds during the two weeks prior to taking it for inspection heats the catalytic convert so that it burns off any residue that has collected in the exhaust. If the car is marginal on passing the inspection, eliminating this residue sometimes provides the needed improvement.
Inflating tires and ensuring fluid levels are full increases the chances of a vehicle passing the test. Testing involves driving the car on a machine while it remains stationary. Underinflated tires increase the stress on the engine. A car that is low on coolant could overheat. If an oil change is due, have it done prior to the inspection; otherwise, add oil to the full mark. Fill the gas tank before heading to the inspection station. Some testing machines place the car at an angle that could expose the fuel pump intake during the test, affecting the fuel-to-air ratio and cause a failure.