Emissions Test Basics
Generally, in an emissions test, there are three different vehicle inspections that could point to a wide variety of causes of a failed emissions test.
- The Acceleration Simulation (ASM) checks for dangerous gases like carbon monoxide.
- The On-Board Diagnostics (OBD) monitors the performance and status of the emission control equipment and the ignition system.
- The Two-Speed Idle (TSI) tests emission gases on older vehicles (those vehicles from 1995 or before).
There are five gases that are monitored during emissions tests: carbon monoxide, carbon dioxide, hydrocarbon, oxygen, and nitrogen oxides. A gas analyzer is put in a vehicle’s tailpipe to measure the emission of these gases. There are also portable gas analyzers which use infrared to measure the temperatures of the various gases. Additionally, diesel analyzers are used to monitor emissions for diesel engines.
The Diagnostic Link Connector (DLC) Scanner works with a Diagnostic Link Connector monitor. Sometimes a vehicle needs to be driven a distance in order for all the monitors of the DLC Scanner to work properly. This means that a car owner will be asked to drive an additional distance before returning so that the DLC Scanner can work properly.
Additionally, the DLC will check if the Malfunction Indicator Lamp (MIL) light is on or off. The MIL light is a signal warning for problems and malfunctions in the engine so it is very important that it be in proper working order and good condition. The MIL light uses the Check Engine Light (or other warning light) to help determine the engine’s status. Usually, the MIL light is turned on when the vehicle’s engine is causing issues that result in excessive emissions. The DLC Scanner also gets any fault codes that the vehicle currently has.
Emission Standards in the US
The US has different standards for each gas that is being monitored. Here are the levels that are used in your car’s emissions standards tests.
- Hydrocarbons—In the atmosphere, hydrocarbons react to the nitrogen oxide and sunlight. The combination produces ozone. On the ground, ozone is a part of smog which is one of the worst offenders of air pollution. Smog can cause breathing problems, damage lungs, irritate eyes, and has even been found to cause cancer.
The amount of hydrocarbons from a passenger car that is a transitional low emission vehicle (TLEV) must be less than .156 g/mi. An ultra-low emission vehicle (ULEV) must have a level that is lower than .055 g/mi.
- Nitrogen oxide—When oxygen and nitrogen combine a high pressure, nitrogen oxide is formed. Engines can be very high producers of nitrogen oxide. Nitrogen oxide is the primary cause of acid rain. The maximum nitrogen oxide level for emissions is .6 g/mi for a TLEV and .3 g/mi for a ULEV.
- Carbon monoxide—When fuel is not completely oxidized to carbon dioxide, carbon monoxide forms. Carbon monoxide is toxic to human beings and it is one of the primary emissions from vehicles. The maximum amount of carbon monoxide for a TLEV is 4.2 g/mi and for a ULEV the maximum amount is 2.1 g/mi.
- Carbon dioxide—This gas is one of the main greenhouse gases that contribute to the increase in the earth’s overall temperature.
- Additional emissions—Some of the emissions are created by evaporation that occurs at higher temperatures. For example, gas vapors are vented at higher temperatures. For emissions testing, the emissions of gas vapors must be less than 2.0 g/test hour.
- Additional standards—Each state has additional standards that must be met for emissions tests.
Common Failure Reasons
There are several causes of a failed emissions test. Here are a few of the more common reasons. If you need to have an emissions test or need a repair to pass your emissions test, contact us at Sundance Automotive in Westminster to make an appointment.
- Fuel metering specification. Your vehicle could have a faulty computerized engine control, fuel injections unit, or carburetor that can cause your vehicle’s fuel metering to not meet specifications.
- Faulty oxygen sensor. A faulty oxygen sensor is very common and can lead to other problems such as higher emissions, overheating, and loss of acceleration.
- Defective ignition system. Generally, this means your car is emitting high amounts of hydrocarbons. It can be an indication of defective spark plug wires, worn out spark plugs, a worn distributor cap, or an ignition-timing problem.
- Vacuum leaks. The MAP sensor not working properly can lead to a leak and be one of the causes of a failed emissions test.
- Rich fuel mixture. A rich air/fuel mixture can be caused by a number of issues such as leaky injectorsor excessive fuel pressure. This will cause high carbon monoxide levels as well as high carbon dioxide emissions.
- Malfunction in the air injection system. This system reduces the emissions of hydrocarbons and carbon monoxide. The air injection system forces air into an engine’s exhaust. If this system is not working properly, the vehicle can emit large amounts of carbon monoxide and hydrocarbons.
- Faulty evaporative emission control system. The evaporative emission control or EVAP system prevents gasoline vapors from being released into the atmosphere. Leaks in system hoses and vents are common reasons for this system to be problematic. It could also be related to a defective purge valve or a faulty gas cap.
Hopefully, now that you know the causes of a failed emissions test, you’ll be better prepared and a little less worried if and when your car experiences an issue. Most importantly, you can always bring it to Sundance Automotive in Westminster to get the repairs handled by the pros. Contact us today for your appointment and we’ll make sure your car aces the test next time around.