Emission Control Glossary

Acoustic Tube Located in the muffler, the acoustic chamber is specifically designed to help "tune" exhaust noise energy as well as convert it into heat. Baffles located inside the muffler interact with exhaust pressure waves to produce specific noise frequencies. By adjusting the size and shape of acoustic chambers, exhaust noise can actually be tuned, much like an instrument.

Activated Charcoal The Evaporation Emissions Control (EVAP) system relies heavily on activated charcoal as an absorber and storage vessel for fuel vapors. Both shoe inserts and a charcoal canister take advantage of charcoal's ability to readily absorb vapors. As fuel molecules heat and vaporize, they travel down a re-cycling tube and enter the canister through a one-way valve. When the engine is turned back on, a vacuum is created that sucks the reconstituted vapors out of the canister and into the engine where it is burned.

Air-Fuel Ratio Air and fuel are mixed into a highly combustible vapor before being burned in the engine. The measure of air and fuel is represented as a ratio. The air/fuel ratio is not a static measure but rather changes to meet performance demands.

Auto Emissions Your engine burns gas to create the power needed to power your automobile. During the process, it creates pollutants that can be harmful if inhaled as well as damaging the environment. Your engine produces four basic types of pollutants:
· Carbon Monoxide
· Hydrocarbons
· Oxides of Nitrogen
· Particulates

Air Injection System A critical part of the emissions control system, the air injection system begins to eliminate residual fuel vapors as soon as they exit the engine. By adding a small amount of fresh air to exhaust as it exits the engine, residual fuel vapors are allowed to continue to burn as they travel through the exhaust manifold toward the catalytic converter.

Air Pump Many modern vehicles use an air pump to send compressed air into the exhaust manifold. This air helps convert poisonous carbon monoxide in the exhaust into less dangerous carbon dioxide

Back Pressure Anything that inhibits exhaust from quickly exiting the exhaust system contributes to a condition known as back pressure.

Bad Air Injection Diverter Valve Normally, the air injection diverter valve keeps air from entering the exhaust during deceleration, which prevents backfiring. Backfiring frequently happens when you take your foot off the gas pedal and begin to slow down or decelerate. When the diverter valve goes bad, the diverter fails to properly seal, and allows air to mix with residual fuel vapors present in the exhaust, causing a mini explosion in the exhaust that we call a backfire.

Bad Catalytic Converter The catalytic converter is an emissions control device installed in the exhaust system, just prior to the muffler along the undercarriage. Over time the catalyst can break apart and cause a rattle that can sound similar to a loose exhaust clamp. The catalysts can also become covered in a layer of chemical deposits that reduce its ability to burn off harmful emissions.

Blown Head Gasket A head gasket is the seal between the engine block and cylinder head. This gasket keeps coolant from leaking into the cylinders and free from contamination by exhaust gases. A leaking head gasket will allow coolant to seep into the cylinder and burn, producing a white-ish colored exhaust. A 'blown' head gasket is a leaking gasket and causes a loss of compression.

Broken Exhaust Clamp Exhaust clamps are U-shaped bolts that connect one portion to the exhaust to another. Over time clamps can become fatigued and are subject to break or come loose.

Broken Exhaust HangerTo support the length of the exhaust system, hangers secure the exhaust system to the underneath of the vehicle. Over time hangers can become fatigued and are subject to break or come loose. When they do come loose, the exhaust has a tendency to rattle or bang against the bottom of the car, particularly when going over bumps or striking potholes. Over time more hangers may give way under the increase in relative weight that each surviving hanger must support. If the condition is left to deteriorate, you may find yourself dragging your exhaust after hitting a pot hole.

Burning Coolant Burning coolant occurs when coolant enters the engine's cylinder and is burned along with the air/fuel mixture. Frequently the cause of an engine burning coolant is a cracked (blown) or warped head gasket. However, small cracks in the engine itself can also be cause. An engine that is burning coolant will have a white-ish or gray exhaust.

Burning Oil Burning oil occurs when oil is allowed to enter the engine's cylinder and is burned along with the air/fuel mixture. Worn piston rings are a common cause of burning oil. An automobile that is burning oil will tend to emit exhaust that has a bluish tint and may be a little heavier than normal.

Combustion Process The combustion process is an extremely well orchestrated event that brings together a highly volatile mixture of air and fuel and an electric spark. The resulting explosion provides kinetic energy which your automobile is designed to harness in the form of locomotion.

Carbon Contaminated Sensor Carbon contamination occurs when oil is burned in the engine during the combustion process. Burnt oil particles (carbon) will gradually coat an oxygen sensor and in time may cause the sensor to malfunction.

Carbon Deposits

Carbon Dioxide Carbon dioxide is the fourth most abundant gas in our atmosphere and forms naturally as a by-product of respiration, or breathing. However, over the years, carbon dioxide has been called one of the Earth's so-called greenhouse gases. According to the greenhouse theory, as more carbon dioxide is produced, it creates a thickening invisible layer that shrouds the earth, reflecting infrared radiation emitted by the sun and slowly begins a general warming process.

Carbon Monoxide Carbon monoxide is an extremely dangerous emission that can suffocate unsuspecting motorists if they let their vehicle run in a un vented space like a garage. Inhaling carbon (CO) can cause nausea, headaches and extreme fatigue and is particularly dangerous because it is both colorless and odorless and difficult to detect. CO is formed when partially burned fuel is released.

CO Carbon monoxide is an extremely dangerous emission that can suffocate unsuspecting motorists if they let their vehicle run in a un vented space like a garage. Inhaling carbon (CO) can cause nausea, headaches and extreme fatigue and is particularly dangerous because it is both colorless and odorless and difficult to detect. CO is formed when partially burned fuel is released.

Catalyst Catalyst is just a name for something that causes a chemical reaction without neutralizing itself. Your catalytic converter is lined with catalysts like aluminum oxide and platinum that react to the harmful gases found in exhaust and changes them into water vapor, nitrogen and carbon dioxide.

catalytic converter The catalytic converter is a smog reduction device located between the exhaust manifold and the muffler. The converter reduces harmful emissions by converting, or neutralizing these gases into harmless carbon dioxide and water. Central to its function is the role of catalysts.

Catalytic Core

Clogged Exhaust System The exhaust system can sometime become clogged from loose debris, such as broken catalyst from the catalytic converter. Any sort of clog or restriction of auto exhaust can cause a condition known as back pressure.

Combustion Chamber A small space located at the top of the cylinder where the spark plug is screwed into the cylinder head.

Computer Module any electronic circuit that can receive signals (inputs) or modify a signal and find outputs. Finding outputs is just another way of processing information or signals.. " Module ” is often a more specific way of talking about a particular system.

Crossover Pipe Most vehicles have only one muffler and catalytic converter. After gas exits the exhaust manifolds, the crossover pipe funnels exhaust from one side of the vehicle to the other for entry into the single catalytic converter.

Cylinder The cylinder is the round tube in the engine block in which the pistons move up and down.

Data Port Data ports (data links) are connections that allow diagnostic computers (scan tools) to plug into an automobile's computer system and retrieve trouble codes and sensor readings. Data ports are rectangular plastic connectors with multipin receptacles

Defective Oxygen Sensor In time oxygen sensors can begin to malfunction and provide incorrect data or stop working altogether. Defective oxygen sensors can cause engine performance to suffer as well as permit excessive auto emissions. Common causes of a defective sensor include, sensor contamination, a wire short or an computer module fault.

Disconnected Exhaust The exhaust system is susceptible to corrosion, which leads to rust holes, rusted seams, and frequently leads to exhaust system replacements and repairs. As part of the corrosion process, it is not uncommon for the exhaust to become disconnected.

Dual-Bed Catalytic Converter The catalytic converter is a smog reduction device located between the exhaust manifold and the muffler. The converter reduces harmful emissions by converting, or neutralizing these gases into harmless carbon dioxide and water. Most honeycomb block designs are divided into two separate blocks, called a dual-bed catalytic converter. The dual bed converter uses injected air to help burn pollutants during the process.

Dual Exhaust With two mufflers, catalytic converters and tailpipes, dual exhaust allows the engine to “breathe” more freely. Vehicles with dual exhaust have no need for a crossover pipe and often see an increase in horsepower. Dual exhaust removes more fumes from the combustion chambers, leaving more room for air and fuel intake.

EGR Valve Many modern vehicles use an Exhaust Gas Recirculation valve to send some exhaust back into the combustion chambers. When combustion reaches temperatures above 1,400°, smog-forming nitrogen oxides are formed. Recycling a small amount of exhaust into the chambers reduces combustion temperature, so less poisonous gas is produced

Emissions Control Emissions control is concerned with reducing the amount of harmful substances that are released into the atmosphere by combustion engines.

Engine Control Module The engine control module is one of the primary computer modules. It helps coordinate the operation of the engine and can tweak performance based on sensor readings. The engine idle, fuel injection, emissions and ignition timing can all be controlled with the engine control module

Engine In-tune A state in which the engine's ignition timing, spark plugs and filters are in a condition to deliver optimal engine performance.

Engine Performance Broadly speaking, engine performance is a qualitative measure of anything that has to do with how the engine operates. While a bit of a general term, engine performance tends to include concepts like fuel economy, power production, ignition timing and auto emissions.

Exhaust Emissions Exhaust emissions are the by product of burning air and fuel during the combustion process.

Evaporation Emissions Control The Evaporation Emissions Control (EVAP) system is designed to function as a closed loop recycling system to prevent fuel vapors from leaking into the atmosphere.

Exhaust Gas Recirculation The exhaust Gas Recirculation (EGR) system was developed as a way to recycle exhaust fumes and prevent the formation of Oxides of Nitrogen (NOx). NOx forms when fuel is burned at an extremely high temperature. The EGR system lowers combustion temperatures by diluting the oxygen level of the air entering the engine, thereby reducing temperatures.

Exhaust Gas Recirculation ValveMany modern vehicles use an Exhaust Gas Recirculation (EGR) valve to send some exhaust back into the combustion chambers.

Exhaust Hangers Metal hangers are used to support and secure the length of the exhaust system to the underside of the vehicle.

Exhaust ManifoldA series of gently curving, cast iron pipes that accept exhaust from the combustion chambers. Gases move from the exhaust manifold to the catalytic converter for neutralization.

Exhaust Pipes Slightly curving metal pipes that connect the exhaust manifold, catalytic converter and muffler. Exhaust pipes provide a means to evacuate engine exhaust to the rear of the automobile.

Exhaust System The exhaust system quiets and neutralizes exhaust gases that are by-products of the combustion process. A series of metal clamps, joint solders and rings hold the system is place and give it flexibility and added noise insulation.

Faulty Air Injection Diverter Valve Normally, the air injection diverter valve keeps air from entering the exhaust during deceleration. When the diverter valve goes bad, the diverter fails to properly seal, and allows air to mix with residual fuel vapors present in the exhaust, causing a mini explosion in the exhaust that we call a backfire.

Faulty EGR SensorThe EGR reduces nitrous oxide emissions. But if either the valve or the valve sensor fail, the system is unable to regulate the proper flow of exhaust gas and as a result your vehicle may be emitting higher NOx levels than permitted by law.

Faulty EGR System During the combustion process, temperatures can get very hot. If the temperature reaches 2,500 degrees or more nitrous oxide (NOx) forms. Nitrous oxide is a major contributor to smog. So to help reduce combustion temperatures, exhaust is recycled and mixed with the air fuel mixture before it is sent into the combustion chamber and burned. By simply diluting the percentage of oxygen rich fresh air present in the air /fuel mixture, nitrous oxide emissions can be reduced. The EGR valve is responsible for regulating the flow of exhaust gas into the intake manifold. A small electronic sensor is built into many valves to determine EGR valve position and sometimes gas flow. But if either the valve or the valve sensor fail, the system is unable to regulate the proper flow of exhaust gas and as a result your vehicle may be emitting higher NOx levels than permitted by law.

Faulty EGR ValveThe exhaust gas re circulation, or (ERG) system was designed to reduce harmful exhaust emissions.

Faulty Fuel Pressure Regulator The fuel pressure regulator works with the fuel pump to deliver the proper amount of fuel to the fuel injector. However, too much fuel can cause an adverse affect on engine performance. If too much fuel enters the engine, residual fuel molecules will enter the exhaust system.

Faulty Valve Guide Engine valves are operated by a stem that moves up and down inside a hole called a valve guide. To keep oil from leaking down the valve stem and entering the combustion chamber, a rubber valve seal is seated in the valve guide. Through extended use, the valve guide can become worn or damaged and allow oil to enter the combustion chamber. Worn valve guides also tend to increase valve noise.

Fuel Efficiency Fuel efficiency (fuel economy) is a measure of comparing the number of miles your automobile can drive on one gallon of gas to the estimated Miles Per Gallon (MPG) of the manufacturer.

Haagen-Smit Arie A onetime perfume developer and bio-chemist would go on to become known as the “Father of Pollution Control." In 1948 Dr. Haagen-Smit became alarmed at the continued damage to his plants, such as discolored leaves and undersized flowers. In 1952 Dr. Arie Haagen-Smit discovered the nature of photochemical smog, determining that nitrogen oxides and hydrocarbons combined with ultraviolet radiation from the sun created smog. He also discovered that ozone played a key role in the bonding process that created smog. Today's nationwide air pollution air quality standards based are based directly on Dr. Haagen-Smit's research.

HC Hydrocarbons (HC) are present in petroleum products like gas and oil and can be emitted into the atmosphere either through the combustion process or through simple evaporation, such as gas evaporating from a worn fuel cap seal.

Heat Shield The exhaust system handles both hot engine exhaust and generates additional heat through the operation of the catalytic converter. To protect the underneath of the automobile, and heat sensitive parts and wiring, a heat shield is installed. Constructed of sheet metal or fiberglass, heat shields are a protective barrier against the damaging affects of heat.

Hole In The Exhaust The exhaust system is susceptible to corrosion, which leads to rust holes, rusted seams, and frequently leads to exhaust system replacements and repairs. one of the first indications of a hole in the exhaust is a change in the sound quality of their exhaust system.

Houdry Eugene Although Houdry was born in France, in time he imigrated to the United States. Houdry distinguished himself as a soldier during WWI and received one of Frances highest medals honor. As and inventor, Houdry's inventions were no less dramatic and ranged from a synthetic form of rubber to the catalytic converter and a revolutionary process that allowed high grade gasoline to be produced from low-grade crude oil.

hydrocarbons Hydrocarbons (HC) are present in petroleum products like gas and oil and can be emitted into the atmosphere either through the combustion process or through simple evaporation, such as gas evaporating from a worn fuel cap seal.

Ignition Fault

Ignition Module The Ignition Control Module is responsible for both monitoring and managing the ignition system operation. The module takes the place of traditional distributor-based ignition systems.

Incorrect Air-Fuel Ratio Air and fuel are mixed into a highly combustible vapor before being burned in the engine. The measure of air and fuel is represented as a ratio. An improper air/fuel ratio will cause engine performance to suffer and fuel efficiency to decline.

Incorrect Ignition Timing The engine's timing is critical for optimal engine performance and is a highly choreographed event involving the engine's valves, pistons, ignition system and fuel delivery. If the spark is delivered too early, it will burn the fuel prematurely causing the engine to ping, also called pre ignition or knocking. By contrast, if ignition occurs too late, the engine will lack power.

Indicator Light Indicator lights (warning lights) alert drivers when a problem or condition occurs. Sensors located throughout your automobile are constantly monitoring events or conditions and reporting data readings back to a computer module. If a sensor reading appears out of a pre-determined range, a warning light may illuminate on the instrument panel to alert the driver.

Intake Manifold The intake manifold is found in carbureted engines and is responsible for accepting air and fuel from the throttle body. Air and fuel are routed from the intake manifold to each of the engine cylinders via passages called "runners."

Kettering Charles Ketterings inventions ranged from the electric cash register to the spark plug and safety glass. But perhaps his best known invention was the electric automobile starter.

Lead Contaminated Oxygen Sensor Lead contamination occurs when a film of lead deposits coat the ceramic tip of the sensor. The thin lead coating interfers with the sensors ability to produce enough voltage output to signal the control module.

Leaking Fuel Injector The fuel injector is responsible for delivering just the right amount of fuel to the engine. Overtime fuel injectors can develop a leak. Leaking injectors allow too much fuel to be present during the combustion process. The source of a leaking fuel injector can frequently be narrowed down to about three potential things, dirty fuel injector valves, weak or broken return springs, or deteriorating seals.

Loose Exhaust Clamp Exhaust clamps are used to connect one portion of the exhaust system with another. Over time exhaust clamps can break or come loose. When clamps come loose they allow parts to rattle and may even permit portions of the exhaust to become disconnected.

Loose Heat Shield The engine’s exhaust is extremely hot as it exits the combustion chamber and as a result, great deal of heat is absorbed by the exhaust system. To protect heat sensitive components from the intense heat, shields we developed. Over the life of the car, the bolts connecting the hear shield to the bottom of the vehicle can gradually come loose, allowing the shield to vibrate against the under carriage.

Loss Of Power A loss of engine power causes the vehicle to accelerate slowly or can also mean that the engine is unable to achieve top speeds. The source of a sluggish engine or a loss of power can be caused by a problem in the ignition, fuel or emission control systems.

Malfunctioning Oxygen SensorThe oxygen (O2) sensor monitors levels of oxygen present in the engine's exhaust and transmits data readings back to the onboard computer. However, if the O2 sensor begins to fail, it will report incorrect data, which in turn causes the computer to make incorrect adjustments.

Misfire A misfire occurs when one or more of the cylinders fails to fire. Or in other words, the air/fuel mixture did not combust. Misfires can occur at idle, acceleration or even while driving at highway speeds.

Missing Exhaust Clamp

Muffler The muffler 'muffles' exhaust noise by reducing its pressure. Gas rushes through zigzagging or perforated chambers and is converted to heat before release into the atmosphere.

Noise Cancellation Holes located in accustic pipes allow sound waves to exit in a variety of directions, causing the pressure waves to collide in to one another and help cancel each other out. As pressurized gases bump and bounce through the muffler's chambers, their noisy energy is further dissipated and converted into heat.

O2 Sensor Fault Oxygen sensors have a normal lifespan or around 50,000 miles and over time contaminants such as excess carbon or leaded fuel can coat the sensor and cause a false oxygen reading. Once contaminated with a coating of carbon or other substances, the oxygen sensor tends to send incorrect data to the control module. As a result, the engine control module will tend to make improper adjustments that adversely affect engine performance and fuel efficiency. In addition, auto emissions may become excessive.

Oil Contaminated Oxygen Sensor Oil contamination occurs when oil is burned in the cylinder and the oil laced exhaust creates a residue on the oxygen sensor.

Onboard Computer "On-board computer" is a frequently heard generic term for an automobile's computer system. A computer is any electronic circuit that can receive signals (inputs) or modify a signal and find outputs. Finding outputs is just another way of processing information or signals.. " Module ” is often a more specific way of talking about a particular system.

On-board Diagnostics The term "on-board diagnostics" refers to the ability of the automobile's computer and sensory systems to constantly monitor and manage the various automobile systems and indicate the cause of a problem when it occurs.

On-The–Fly On-the-fly is a term that means something happens automatically or occurs without stopping. While driving, your automombile's computer system constantly makes on-the-fly adjustments to optimize performance.

Midgley Thomas A mechanical engineer and self taught chemist, Thomas Midgley had a distinguished carreer at General Motors and was involved with some of the most popular and some might say infamous developments in automotive history. Aided by Charles Kettering, Thomas Midgley invented a compound called Freon. Freon was a popular refrigerant used until its ban years later as part of chemical class of chemicals called Chlorofluorocarbons (CFCs) or green house gases. In addition, Midgley also developed the use of tetraethyl lead. For over 50 years lead was added to gasoline as an anti-knock agent before its final ban due to environmental concerns.

Nox Catalytic converters are designed to burn around 1,400 degrees Fahrenheit. If temperatures increase above that amount, oxygen and nitrogen can combine into oxides of nitrogen, a major contributor to smog.

Nitrogen Oxide Exhaust flows through the exhaust system, and eventually entering the catalytic converter. A chemical reaction occurs inside the catalytic converter that causes it to operate like a mini furnace, burning excess fuel particles before being emitted into the atmosphere. Catalytic converters are designed to burn around 2500 degrees Fahrenheit. If temperatures increase above that amount, oxygen and nitrogen can combine into oxides of nitrogen, a major contributor to smog.

Oxygen Sensor Fault The O2 sensor measures the amount of oxygen present in the engine’s exhaust as a way to monitor combustion efficiency. However, a faulty sensor will provide incorrect data and cause engine performance to suffer.

Particulates As the name implies, particulates are simply the by-product of the combustion process and consist of small solid particles that get blown out the exhaust.

PCV Valve Many modern vehicles use a hose to connect the engine and intake manifold. This hose draws out corrosive gases before they cause rust and sludge in the crankcase. The Positive Crankcase Ventilation valve controls the release of gas into the intake manifold, which can also prevent an explosion in the crankcase if the car backfires.

Positive Crankcase Ventilation The PCV system both relieves crankcase gases and reduces emissions by simply recycling the fumes.

Purgeline The Purge Line connects The Charcoal Canister To The Intake Manifold

Reduction Catalyst

Resonator The resonator acts like a small, straight-through muffler, located near the rear of the automobile, between the muffler and tail pipe. It is designed to quiet noisy exhaust that made it through the muffler.

Rusted Muffler The exhaust system will generally rust from the inside out. Within the muffler, the baffles, which are designed to help reduce exhaust noise, are often the first component to rust out. As they deteriorate, rust residue is blown through the tail pipe. Consequently, the first indication of a rusting exhaust system is a change in the sound quality of their exhaust system.

Rusting Exhaust System The exhaust system is susceptible to corrosion, which leads to rust holes, rusted seams, and frequently leads to exhaust system replacements and repairs. The exhaust system will generally rust from the inside out.

Scan Tool An electronic device used to access and interpret diagnostic automotive codes and sensor readings. Most scan tools are relatively small and a designed to be handheld.

Silicone Contaminated Sensor Silicone contamination occurs when too much silicone sealer was used during an engine rebuild. The excess sealer is burned and the silicone residue coats the oxygen sensor.

Smog Smog looks like a mixture of smoke and fog, which is why it's called smog. It is made up of particulates, which are formed by a complex reaction between oxides of nitrogen and a wide range of hydrocarbons, which is triggered by sunlight.

Tail Pipe A relatively short section of metal pipe that transports exhaust from the muffler or resonator into the atmosphere.

Tetraethyl Lead (TEL) Lead was a common anti-knock fuel additive from 1921 until its final ban in 1985.

Trouble Code Sensors located throughout your automobile are constantly monitoring events or conditions and reporting data readings back to a computer module. If a sensor reading appears out of a pre-determined range, a special code is stored in the automobile's computer system. Trouble codes provide information about the nature of the problem and can frequently assist a service technician in determining the specific source of the problem. Trouble codes are retrieved by a handheld diagnostic computer called a scan tool

Troubleshooting Troubleshooting is a systematic attempt to solve problems. Initially problems are identified and then a process of problem resolution is initiated. Frequently, troubleshooting involves the use of a diagnostic flow chart that provides a step by step process of testing and ruling out potential causes.

Warning Light Indicator lights (warning lights) alert drivers when a problem or condition occurs. Sensors located throughout your automobile are constantly monitoring events or conditions and reporting data readings back to a computer module. If a sensor reading appears out of a pre-determined range, a warning light may illuminate on the instrument panel to alert the driver.

Worn Piston Ring To help create a seal around the piston a series of metal rings are seated in manufactured grooves on the piston head, called piston rings. Over time piston rings can become worn and result in decreased engine compression and a general loss of power. In addition, worn piston rings frequently allow oil to seep into the engine's cylinder and be burned.

Valve Guide Seals


More Emission Control Information:

Emission Control System Overview
Emission Control Milestones In Auto History

General Information

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