THE VISUAL INSPECTION

The smog-check process begins with a visual inspection of the emissions-related components of a car. The technician will verify that the required components exist and are connected properly. In particular, this inspection will look for defective or disconnected electrical connections, hoses, pipes, and other plumbing that may affect engine performance or increase harmful emissions.

THE EMISSIONS INSPECTION

This portion of the test involves analyzing the actual emissions of your vehicle. The test is designed to ensure that fuel in the combustion chamber is burning efficiently and cleanly. Smog is formed due to improperly burned fuel. Typically, this is due to either too much fuel or too little fuel being fed into the engine. Too much fuel can lead to high levels of carbon monoxide (CO); too little can lead to high levels of nitrous oxide (NOX). The engine may also misfire due to inadequate fuel, creating excessive hydrocarbons (HC).

In areas of California where smog pollution is higher, vehicle owners are required to complete an "enhanced" version of California's smog test. The enhanced smog test requires your vehicle to be driven on a dynamometer while the smog machine collects emissions samples from the tailpipe. This test provides a more accurate sample of a vehicle's emissions output than the "basic" smog test. The basic smog test requires vehicles to be tested only at idle and at 2500 RPMs.

VISIBLE SMOKE TEST

Beginning in March 2008, any vehicle given a smog-check inspection will also be required to undergo a visual test for smoke. This test is in addition to the standard tailpipe emissions test.

THE FUNCTIONAL INSPECTION

The functional inspection is performed by the smog technician and includes an examination of the following components:

• Check Engine Light
• Gas Cap & Filler
• Ignition Timing (if applicable)
• Exhaust Recirculation Valve - EGR (if applicable)
• Fuel EVAP Test (LPFET)
• Check Engine Light

CHECK ENGINE LIGHT

A check engine light that is illuminated indicates a problem with the vehicle and in most cases will prevent your car from passing a smog check. Vehicle manufacturers have placed the check engine light inside the passenger compartment to inform the driver of an engine or drive-train malfunction. Even if you do not notice an engine problem while driving, the condition should be diagnosed as soon as possible by a reputable and certified smog-check repair station. Repair stations can be found at the Bureau of Automotive Repair Website (http://www.smogcheck.ca.gov).

GAS CAP & FILLER

Your vehicle's gas cap and filler neck will also be inspected. The gas cap and tank must be able to hold pressure at factory specifications and the filler neck must not be altered to accept leaded gas. If your gas cap appears to be loose or broken, Smog Man will replace it for you free of charge.

IGNITION TIMING

The next inspection is the ignition timing check. During this exam the smog technician will ensure that your engine is supplying electric current to the spark plugs at the correct time in the cycle. In some newer vehicles, the timing is computer-controlled and so this manual check is not required. You can find out if your vehicle requires a timing inspection by reading the emissions label, which is typically located on the bottom panel under the hood.

If this test is required for your vehicle, you can perform it yourself at home with a timing light and minimal mechanical experience. Timing lights are available at auto-parts stores in your area. Check the emissions label under the hood for timing specifications and procedures. The following early model vehicles have timing settings: Acura, Audi, Buick, Chevrolet, Chrysler, Dodge, Plymouth, Fiat, Ford, GM, GMC, Saturn, Honda, Hyundai, Infiniti, Isuzu, Jaguar, Jeep, Lexus, Mazda, Mercedes Benz, Mitsubishi, Nissan, Peugeot, Porsche, Renault, Land Range Rover, Saab, Saturn, Subaru, Suzuki, Toyota, Volkswagen, VW, and Volvo.

EGR VALVE

Some vehicles are also required to undergo an Exhaust Gas Recirculation (EGR) valve inspection. The EGR system recirculates partially burned exhaust gas back into the combustion chamber and mixes it with fresh fuel. This process reduces the amount of real fuel in the chambers, thus lowering operating temperatures and reducing NOX emissions. The high demand for air during the intake cycle creates a vacuum in the engine's intake manifold. A functional EGR valve should be able to open using this manifold vacuum.

Over time, carbon buildup may impede the normal functioning of this valve. Some vehicle manufacturers recommend cleaning this component on a regular basis. The following late-model vehicles are equipped with EGR systems: Acura, Audi, Buick, Chevrolet, Chrysler, Dodge, Plymouth, Fiat, Ford, GM, GMC, Saturn, Honda, Hyundai, Infiniti, Isuzu, Jaguar, Jeep, Lexus, Mazda, Mercedes Benz, Mitsubishi, Nissan, Peugeot, Porsche, Renault, Land Range Rover, Saab, Saturn, Subaru, Suzuki, Toyota, Volkswagen, VW, Volvo, and Winnebago.

LOW PRESSURE FUEL EVAP TEST (LPFET)

Beginning in November 2007, model year vehicles 1976 to 1995 will be required to undergo an additional test called the Low Pressure EVAP Test (LPFET). This test is designed to ensure that your vehicle's fuel evaporative system is not leaking gas fumes into the atmosphere. The test applies to all pre-OBD II vehicles that are required to have smog checks.