Car whisperer

How to keep your car from failing a SMOG test

Sooner or later most vehicles are required to pass a SMOG certification. How can you make sure your vehicle aces the exam?

"The easiest way to pass a SMOG test is to have your Toyota serviced regularly," said Tony Molla, vice president of communications at the National Institute For Automotive Service Excellence. "This will identify problems that affect the way your Toyota performs before you spend time in the SMOG test lane."

In 1984, California initiated SMOG tests as part of a statewide campaign to reduce air pollution, especially in the Los Angeles basin. Today, most states have SMOG testing but requirements vary.

Pollutant level

Maintenance The tests determine amounts and types of pollutants coming out of your vehicle's tailpipe. Results are directly related to the health of your vehicle.

"The Emissions Control System in a vehicle conducts a balancing act to maintain engine performance," Molla said. "It always adjusts the air-to-fuel ratio, which affects how your car operates and also its ability to pass a SMOG test."

As an example, the ECS adjusts for driving speed and temperature. Other factors include changes in altitude, octane of gas and age of engine components. Worn out parts could cause your vehicle to fail a SMOG test.

Loose or corroded distributor wires found on an older vehicle can cause it to fail a SMOG test. Yet, the parts are easy to spot and simple to replace during routine check-ups.

The test involves connecting a hose to the vehicle tailpipe. Exhaust fumes are analyzed by computer and compared against limits set by the State Air Resources Board.

Figuring out what caused a test failure is harder, however. SMOG readings show levels of pollutants such as nitrogen oxide, carbon monoxide and hydrocarbons. The results do not indicate why the levels are higher than required.

Deciphering clues

Certified SMOG technicians act a bit like Sherlock Holmes. They must interpret data and clues to solve the mystery of why your vehicle didn't pass its SMOG exam.

Maintenance "They are among the most highly trained mechanics because they need extensive knowledge about a lot of different vehicle systems," Molla said.

Modern gasoline engines utilize an Exhaust Recirculation System to capture and eliminate exhaust before it leaves the tailpipe. Leftover fumes are burned by the catalytic converter and carbon dioxide is trapped in filters. The result: Exhaust particles responsible for SMOG are reduced dramatically.

"Sometimes your vehicle may require a simple fix such as unclogging the Exhaust Recirculation Valve or a vacuum hose may be loose," Molla said. "Other times a SMOG test failure could point to a more significant problem such as a malfunctioning catalytic converter or vehicle in need of a tune-up. "

Molla had the following advice for drivers who face an upcoming SMOG test:

Your vehicle could fail a SMOG test simply because it does not have fresh oil and filters. Ask your service advisor how often you need to change the oil, oil filter and air filters to assure peak performance.
Use the grade of fuel recommended by the vehicle manufacturer. It helps the engine burn fuel more efficiently and cleaner.
Call your service advisor immediately if you see a "check engine" light. This may indicate a serious problem with the emissions control system or sensor that has worn out. In either case, don't bother going to the SMOG station-your vehicle will not pass the test.
Complete any manufacturer's scheduled maintenance before getting the SMOG test. Regular maintenance will address problems such as loose hoses, old spark plugs and engine tuning.
In states such as California a "Test-Only" station may only test vehicles for compliance. They are prohibited from making repairs.
In contrast, a "Gold Shield" SMOG station may test your vehicle and make necessary repairs.
The California Department of Motor Vehicles requires a SMOG check every two years. It also requires a SMOG check if you sell your vehicle and it is more than four years old.
Some vehicles in California are exempted from SMOG check requirements. Among them are diesel vehicles, motorcycles, electric and hybrid vehicles and two-cylinder engine vehicles.

"Almost 100% of well-maintained vehicles will pass a SMOG check," Molla said. "Regular maintenance is the easiest way to avoid surprises at the SMOG test station."

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