Why You Failed a Smog Test Check

January 27, 2012

A regular smog text check is as important as having your vehicle checked for any damages or having your car repaired. Certain vehicles are often required to undergo a smog test to check the levels of smog their vehicle is emitting. This is to comply with the laws and regulations by the Bureau of Repair Vehicle and DMV.

Checking for Dangerous Gases

One of the main reasons why vehicles are asked to undergo a smog check is to monitor 5 gases – hydrocarbons, carbon monoxide, nitrogen oxides, carbon dioxide, and oxygen. More often than not, the end result for a smog test to fail is high levels of these gases.

Hydrocarbon is the result of fuel going through a vehicle’s engine without being burned. There are also several causes of hydrocarbon emission while Nitrogen Oxides is the result of excessive heat in the combustion chamber.

On the other hand, carbon monoxide is the result of incomplete combustion in the car’s engine which in turn can cause high levels of oxygen.

Common Reasons

There are certain causes of gas related smog check failures for each of these gases. Common causes of high levels of NOx or Nitrogen Oxides include advance timing and a faulty EGR system. The EGR System or Exhaust Gas Recirculation System is the main component in the exhaust gas recirculation system. It is used to reduce the production of NOx in internal combustion engines. If your vehicle has a faulty EGR system, this may be one of the reasons why your car is emitting high levels of Nitrogen Oxides.

High levels of Hydrocarbons can be due to several causes. Problems with the ignition can be a cause for high HC levels. Parts like the distributor cap and rotor, ignition coil, and wires, as well as the spark plugs that are defective should be replaced or checked to avoid this from happening. Leaks on the gasket can cause vacuum leaks which can also lead to high levels of hydrocarbons. Other causes also include malfunctions on the air or oxygen sensor, engine damage like a burned valve and low compression on the cylinders, and failure on the catalytic converter.

If the fuel metering in your vehicle is out of specification, your vehicle will also fail the smog test. This can be due to a faulty fuel injection unit or faulty computerized engine control system.

Standards on Auto Emissions

Auto emissions standards often differ per state. However, there are certain common guidelines vehicle owners need to follow for them to pass the smog check test. The Environmental Protection Agency or EPA is the agency that handles the standards on auto emissions on a national level.

Some states choose to follow the national guidelines when it comes to emissions standards while others follow the standards set by other states. California is one state that has special dispensation from the federal government to have their own standards. However, states like Vermont, Rhode Island, Washington, Oregon, and Arizona follow California’s emission standards on automobiles.

The nationwide automobile emissions standards were set in 2 tiers; tier I for light vehicles was adapted from 1194 to 1997 while tier II began in 2004 until 2009. There are also standards for heavy duty vehicles which are stricter than light vehicle emissions standards.

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