Smog Certification

Today’s vehicles are sophisticated, computer integrated machines engineered to reduce emissions when in proper operating condition. California State regulations require emissions testing every two years on certain model years. In addition, Los Angeles County is an enhanced emissions testing area. This requires the testing of vehicles with specialized smog equipment that can actually simulate on-road driving conditions. Sun-Fax Auto Repair uses the state-of-the-art ESP System OneĀ® Bar-97 certified five-gas analyzer equipped with a dynamometer and Delphi Evaporative Emissions Tester.

In addition to being a Smog Check Station, our technicians have the capability to diagnose and repair smog failure problems with your vehicles.

Some Smog Inspection Information For Customers…

Basically there are five gases that are monitored when a Smog Check is performed. They are as follows:
…..HC = Hydrocarbons
…..CO = Carbon Monoxide
…..NOx = Nitrogen Oxides
…..CO2 = Carbon Dioxide
…..O2 = Oxygen
Some of the common reasons for Smog Check failures are caused by problems with one or more of these gases.


HC is considered fuel that has gone through the engine without being burned. The emission of this gas also can be caused by various engine conditions or by Smog component failure. A list of causes of HC related Smog Check failure include:

(1.) Ignition Timing Advanced above specifications. Timing is measured in degrees before or after Top Dead Center. If your vehicle is required to be at 10b degrees and instead is set at 16b degrees your HC emissions will increase. (b= before Top Dead Center).

(2.) Ignition system problems. Parts like the ignition coil, distributor cap, distributor rotor, ignition wires and spark plugs.

(3.) Vacuum leaks. Gasket leaks that cause vacuum leaks. Broken, disconnected or misrouted vacuum hoses. Vacuum components failure such as a power brake booster. This causes a very large vacuum leak.

(4.) Catalytic Converter failure.

(5.) Air Injection system problems. (Smog pump and related components).

(6.) Engine damage (burned valve, low or no compression in one or more cylinders).

(7.) Sensor problems and/or computer problems can cause a Smog Check failure.

Nitrogen Oxides (NOx)…

NOx is formed inside the combustion chamber of the engine when excessive heat is present. A list of the common causes of NOx related Smog Check failures include:

(1.) As usual check the timing first. Advanced timing can cause extra NOx.

(2.) The next thing to check is the EGR system. This systems is designed to reduce the NOx. It consists of an EGR valve, vacuum hoses, one or more vacuum switching valves or solenoids. Its job is to reroute a small amount of exhaust gas back into the engine to help reduce combustion chamber temperature. Not all vehicles have an EGR system.

(3.) Next thing to check is the air/fuel ratio. If the vehicle is running to lean, NOx emissions will increase.

(4.) Some other possibilities are a restricted fuel filter, low fuel pressure, vacuum leaks, oxygen sensor, load sensor such as a map sensor, air flow meter.

(5.) Check the cooling system. An extra increase in the water temperature will increase NOx production.

(6.) A defective Catalytic Converter can also increase the NOx. The Cat. reduces NOx that has already been produced.

(7.) Check to see that the air coming into the engine is not over heated. Some vehicles have a vacuum controlled air valve which switches the incoming air to hot air from the outside of your exhaust manifold. This should only happen when the engine is cold. If this system malfunctions and sends hot air all the time, your NOx could go up. This system is called T.A.C. (Thermostatic Air Cleaner).

(8.) There is another system similar to the one above called the E.F.E. (Early Fuel Evaporation). This system routes hot air under the intake manifold. This helps keep the fuel in the vapor state. If stuck in the hot mode NOx could increase and cause a Smog Check failure.

Source for this information is found at: