Repair Info - Emissions Repair Glossary

Emissions repair related terms are listed below in alphabetical order. Scroll down or click a letter below to go to that section of the glossary.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

Aftermarket

A general term referring to auto parts designed to replace defective parts of a vehicle, but made by someone other than a vehicle manufacturer (see also Original Equipment Manufacturer).

Air Cleaner

The plastic or metal assembly that houses the air filter for the engine.

Air Filter

Inside an air cleaner assembly is an air filter that protects the engine from dirt and foreign materials that could damage the engine internally.

Airflow Sensor

Many fuel-injected engines use an airflow sensor or meter to measure how much air is being drawn into the engine. The device measures the volume or mass of air being drawn into the engine and sends that data to the vehicle's on-board computer where it is used to calculate how much fuel is needed to maintain the desired air/fuel ratio.

Air-Fuel Mixture

This phrase refers to the mixture of air and atomized fuel that goes into the engine's cylinders for combustion. To burn efficiently, the mixture must be the correct ratio of air and fuel. See Air Fuel Ratio.

Air-Fuel Ratio

The mixture of air and fuel that goes into the engine's cylinders for combustion must contain a certain amount of fuel in order to burn efficiently. This amount of fuel relative to the amount of air in the mixture is called the air fuel ratio. If the ratio is just right (stoichiometric air-fuel ratio), it can be burned in the engine with maximum efficiency. If there is too much fuel (rich air-fuel ratio), not all of the fuel will be burned completely and high carbon monoxide emissions will result. If there is not enough fuel (lean air-fuel ratio), the combustion of the mixture may stop prematurely and high hydrocarbon emissions will result.

Air-Fuel Sensor

See Oxygen Sensor.

Air Injection System

The air injection system injects air into the exhaust stream. The purpose of this is to promote further oxidation of the exhaust, namely the HC and CO emissions. A common misconception is that the injected air just dilutes the exhaust. In fact, it oxidizes HC and CO into H2O and CO2. Air injection systems include various types of components that affect where and when air is injected into the exhaust system. In many modern vehicles, the air injection system operates only during warm-up.

Air Temp Sensor

Many fuel-injected engines use an air temperature sensor (ATS) to measure the temperature of the air being drawn into the engine. The measured air temperature is indicated to the vehicle's on-board computer. This input is used to calculate how much fuel should be delivered to maintain the desired air/fuel ratio.

ASM

The Acceleration Simulation Mode (ASM) is a vehicle emissions test procedure developed by the US EPA. The test measures emission levels of HC, CO, and NOx while the vehicle is driven at a steady load that simulates maintaining a speed of 40 km/hr while driving up a slight hill. The test may last up to 90 seconds depending on how "clean" the vehicle is in the early part of the test.

Read more about the ASM/Idle test procedure.

Watch a video describing the ASM/Idle test procedure.

B

C

Carbon Dioxide (CO2)

Carbon dioxide is a colorless, odorless gas produced by all animals, plants, fungi and microorganisms during respiration and is used by plants during photosynthesis. CO2 is a normal result of the combustion of fuels. CO2 is the main greenhouse gas produced by human activity.

Carbon Monoxide (CO)

Carbon monoxide (CO) is a poisonous gas that is formed when a carbon fuel is burned incompletely. In motor vehicle emissions, a high CO reading means too much fuel. Fuel can only come from three sources, the crankcase vapor control system, the evaporative control system, or the actual fuel delivery system. See also Causes of Excess Carbon Monoxide.

Carburetor

This is the main fuel delivery component used on most engines built up to the 1988 model year. Carburetors have several sub-systems that cause a different amount of fuel to be delivered to the engine under different operating conditions. A richer than normal mixture is needed during rapid acceleration and also for about the first two minutes of operation after a cold start. For more info on trouble-shooting carburetors, see Fuel System Testing.

Catalytic Converter

By far the most important emissions control component on modern vehicles, the catalytic converter converts most harmful emissions to oxygen, carbon dioxide, and water before they exit the exhaust tailpipe. Some vehicles are equipped with more than one catalytic converter. For more info on trouble-shooting catalytic converters, see Catalytic Converter Testing.

Certified Repair Centre

Repair shops that have the equipment and technicians necessary to perform effective emission repairs can apply to be AirCare Certified Repair Centres. For a vehicle to be eligible for a conditional pass, it must have a Repair Data Form submitted by an AirCare Certified Repair Technician at an AirCare Certified Repair Centre. See also Conditional Pass and Repair Data Form. More about AirCare certification.

Certified Repair Technician

Repair technicians in British Columbia that pass a competency examination administered by the AirCare Program Administration are designated AirCare Certified Repair Technicians. For a vehicle to be eligible for a conditional pass, it must have a Repair Data Form submitted by an AirCare Certified Repair Technician at an AirCare Certified Repair Centre. See also Conditional Pass and Repair Data Form. More about AirCare certification.

Charcoal Canister

This is the main component of a vehicle's evaporative emission control system. This system controls the escape of fuel vapor from the fuel tank. The charcoal canister stores the vapor until it can be burned in the engine at an appropriate time. All vehicles built since the early seventies are equipped with a charcoal canister.

Check Engine Light

1998 and newer light-duty vehicles have On-Board Diagnostic (OBD) systems. If your vehicle finds a problem, it will illuminate the Malfunction Indicator Lamp or MIL, which is commonly called the ‘Check Engine Light’. If the MIL is on when you bring your vehicle in for testing, your car will automatically fail.

Climate Change

Climate change is a shift in long-term average weather patterns, which can include changes in temperature and in precipitation amounts. The international scientific community agrees that there has been a significant change in global climate in recent years, particularly in the polar areas, due largely to the burning of fossil fuels for transportation and industrial processes. These activities emit greenhouse gases that trap heat in the atmosphere.

Combustion Chamber

An area inside the engine where air fuel mixture is drawn into, compressed, and then burned (combustion) to produce power to propel the vehicle. If the combustion chamber has accumulated carbon deposits, high NOx emissions may result.

Compression

The degree to which air/fuel mixture is compressed in an engine's cylinder prior to being ignited. Insufficient compression will prevent proper combustion and power output. A compression test measures each cylinder's compression pressure during cranking conditions.

Conditional Pass

A vehicle that fails re-inspection following diagnosis/repairs by an AirCare Certified Repair Technician at an AirCare Certified Repair Centre receives a conditional pass. A conditional pass enables a vehicle to be re-licensed but it means that an emissions defect still exists on the vehicle. See also Repair Cost Limits and here for more info.

Coolant Temp Sensor

All fuel-injected engines use a coolant temperature sensor (CTS) to measure the temperature of the engine. The measured temperature is indicated to the vehicle's on-board computer. This input is used to calculate how much fuel should be delivered to maintain smooth engine operation when the engine is cold and during warm-up.

Cost Limits

See Repair Cost Limits.

Crankcase Vapour Control System

When an engine is running, oil vapour (and possibly fuel vapour) exists in the crankcase. On all vehicles built since the late 1960s, the Crankcase Vapour Control System prevents this vapour from escaping into the atmosphere. See also PCV Valve.

Cutpoints

See Maximum Allowable Emissions.

D

D147

The D147 is a vehicle emissions test procedure used for measuring opacity from diesel-fueled vehicles. The test measures opacity levels while the vehicle is driven over a pre-defined series of accelerations, decelerations, and cruise conditions. The test may last up to 147 seconds depending on how "clean" the vehicle is in the early part of the test.

Read more about the D147 test procedure.

Watch a video describing the D147 test procedure.

Data Link Connector (DLC)

The interface between a vehicle's OBD computer and the OBD scanner. The DLC is usually located under the dashboard on the driver's side. Connecting an OBD scanner to the DLC allows AirCare inspectors and repair technicians to read the readiness status of the vehicle's various on-board monitors as well as any diagnostic trouble codes (DTCs).

Diagnosis

A diagnosis can actually refer to two things-it is a conclusion that is arrived at after an evaluation of symptoms, and it is also the process of reaching that conclusion. For an in-depth description of both, see What Is A Diagnosis.

Diagnostic Trouble Code (DTC)

Diagnostic trouble code (DTC) is an electronic signal stored in a vehicle's On-Board Diagnostic (OBD) computer, indicating the presence of a fault. 1998 and newer light-duty vehicles are equipped with an OBD system. This is a diagnostic system that continuously checks the condition and operation of key emissions control components and emissions-related systems in your vehicle.

If your vehicle finds an emissions-related problem, it will illuminate the Malfunction Indicator Lamp and store the DTC(s). All manufacturers use the same DTC naming standards. For example, a P0171 Code, means the same thing on a Ford as it does in a Hyundai or BMW.

As OBD systems have been around since 1998, most repair technicians have the equipment and training necessary to read diagnostic trouble codes.

E

EGR

See Exhaust Gas Recirculation.

Emissions Control Equipment

This is a phrase that generally refers to one or several components that are designed to reduce or prevent harmful emissions from a vehicle. Some examples of common emissions control equipment or systems are catalytic converters, oxygen sensors, EGR valves, fuel-injection systems, air injection systems, and gas caps.

Evaporative Control System

Fuel vapours are prevented from escaping into the atmosphere by the Evaporative Control System. The gas cap, tank, charcoal canister, and related hoses and valves are all part of the system. See also Gas Cap and Charcoal Canister.

Exhaust Gas Recirculation

Some engines are equipped with a device or system that recirculates a small amount of exhaust gas back through the combustion cycle under certain operating conditions. EGR systems cool the temperature of combustion, and result in reduced formation of NOx emissions. For more info on trouble-shooting EGR systems, see Exhaust Gas Recirculation System Testing.

Exhaust Muffler

A component in the exhaust system that reduces engine noise.

Exhaust System

A system of components that directs burned gases from the engine, to the rear of the vehicle, and out into the atmosphere. Typical components of the exhaust system include the exhaust manifold (bolted to the engine), exhaust pipes (connecting the exhaust components to each other), and exhaust muffler (the device that reduces the engine exhaust noise). All vehicles built since 1988 (and most built since 1975) also have a catalytic converter in the exhaust. The catalytic converter is the only component of the exhaust system that reduces harmful emissions (the oxygen sensor is attached to the exhaust system but is not generally considered to be a part of the exhaust system).

F

Fuel Cap

See Gas Cap.

Feedback Fuel System

A type of fuel system that is capable of monitoring the air fuel ratio and adjusting it to maintain maximum efficiency. Feedback fuel systems always have an oxygen sensor or an air/fuel sensor to monitor the engine exhaust and provide feedback to the vehicle's on-board computer. Every light-duty vehicle built since the 1988 model year (and some before that) is equipped with a feedback fuel system.

Fuel Delivery System

A general reference to the group of components on an engine that controls how much fuel goes into an engine for combustion. A vehicle's fuel delivery system could be a carburetor, a feedback carburetor, or a fuel injection system. In the case of alternative fuel systems such as natural gas or propane, the carburetor may be called a mixer.

Fuel Injection System

A system of vehicle components that deliver atomized fuel to the engine through small orifices that are usually opened electrically. Fuel injection systems have replaced carburetors on modern engines because they are much more accurate, consistent, and reliable.

G

Gas Cap

The removable cap that allows you to fill your vehicle's tank with fuel. The gas cap is an emission control device because it allows air to be drawn in to the tank but prevents fuel vapors from escaping into the atmosphere.

Gas Cap Test

The gas cap test is a functional test of the gas cap's ability to prevent fuel vapor from escaping into the atmosphere. To pass the test, the cap must hold pressure and must not leak at a rate greater than 60 cubic centimeters per minute. Most vehicles up to and including 1997 model year receive a gas cap test as part of the AirCare inspection. Vehicles newer than 1997 model year that have leaking gas caps are identified using an on-board computer test rather than the traditional gas cap test.

Greenhouse Gases

Greenhouse gases are gases in the earth's atmosphere that trap energy from the sun. One of the key greenhouse gases produced by human activity is vehicular carbon dioxide (CO2). CO2 emissions from light-duty motor vehicles are directly related to fuel efficiency. The more fuel that is burned, the more CO2 emissions are produced.

H

Hydrocarbons (HC)

Hydrocarbon (HC) exhaust emissions are a product of incomplete combustion of a hydrocarbon fuel such as gasoline, diesel, natural gas, and propane. Hydrocarbon emissions can also occur from evaporation of liquid hydrocarbons. HC emissions contribute to the formation of ground level ozone which can cause serious damage to human health and vegetation. See also Causes of Excess Hydrocarbons.

I

Ignition System

Gasoline, natural gas, and propane-fueled engines all require an electrical spark to ignite the air fuel mixture and produce power. The collection of components that generates the spark and controls when it occurs is referred to as the ignition system. Typical components included in an ignition system are spark plugs, ignition coils, and trigger devices such as crank position sensors. Ignition systems on older vehicles require regular maintenance. Modern ignition systems are extremely reliable and typically require less frequent attention than older vehicles. For more info on trouble-shooting ignition systems, see Ignition System Testing.

IM240

The IM240 is a vehicle emissions test procedure developed by the US EPA. The test measures emission levels of HC, CO, and NOx while the vehicle is driven over a pre-defined series of accelerations, decelerations, and cruise conditions. The test may last up to 240 seconds depending on how "clean" the vehicle is in the early part of the test.

Read more about the IM240 test procedure.

Watch a video describing the IM240 test procedure.

Induction System

The induction system is made up of hoses and ducting that may be rubber, plastic or metal, all of which direct outside air into the engine. For more info on trouble-shooting induction systems, see Induction System Testing.

Intake Manifold

The part of the engine between the throttle plate and the cylinder head. The intake manifold directs air and fuel to each of the engines cylinders.

Injection Pump

The main component controlling the injection of fuel into each cylinder of a diesel-fueled engine.

Injection Timing

In a diesel-fueled engine, the time (in relation to piston position) when fuel is injected into the cylinder. If injection timing is incorrect, high opacity (smoke) emissions can occur.

J

K

L

Lean (Air-Fuel Mixture)

A condition where the air-fuel mixture is not the correct ratio (not enough fuel relative to the amount of air). High HC and/or high NOx emissions are symptoms of a lean air fuel ratio.

M

Malfunction Indicator Lamp (MIL)

An illuminated MIL is your vehicle's way of telling you it has found a problem related to the emissions control or engine management systems. The MIL in your car will look similar to one of the examples shown below.

Manufacturers can only use the MIL for indication of emission related faults, and not for maintenance reminders, mileage intervals, or any other non-emission-related items. Generally, the OBD system is required to illuminate the MIL after the same fault has been found in two different driving cycles, which helps to avoid MIL illumination for random faults or abnormal conditions.

If your MIL is commanded on, take it to a repair technician to have the problem addressed before it becomes more serious. Please note, 1998 and newer light-duty vehicles with a MIL commanded on will automatically fail an AirCare inspection.

Manufacturer's Specifications

A specification set by the vehicle manufacturer usually in reference to something that is adjustable or measurable.

MAP Sensor

Many fuel-injected engines use a manifold absolute pressure (MAP) sensor to measure vacuum in the engine's induction system. The device measures the engine vacuum and sends that data to the vehicle's on-board computer where it is used to calculate how much fuel is needed to maintain the desired air/fuel ratio.

Maximum Allowable Emissions

Also known as cutpoints or AirCare standards or AirCare limits, this refers to the emission level that, if exceeded during an official emissions inspection, results in a fail result.

N

NOx

See Oxides of Nitrogen.

O

O2 Sensor

See Oxygen Sensor.

On-Board Computer

All vehicles built since 1988 (and some before that) are equipped with a computer that is designed to control the fuel delivery, ignition, and emission control systems on the engine. The most important function of the on-board computer is to continually adjust the air-fuel ratio so that the engine runs with maximum efficiency (lowest emissions, maximum fuel economy, maximum power, and smoothest idle). See also Feedback Fuel Control.

On-Board Diagnostic (OBD) System

All 1998 and newer light-duty vehicles are manufactured with an On-Board Diagnostic (OBD) system. All manufacturers use the same type of connector, communication protocol and trouble code-naming standard. The OBD system continuously checks the operation of key emissions control components and emissions-related systems in your vehicle.

If the system detects a fault that could cause emissions to exceed one and a half times the federal new vehicle standard for the model year and type, the dashboard Malfunction Indicator Lamp (MIL) will be illuminated on command from the Powertrain Control Module (PCM). The MIL is also commonly called the Check Engine Light. If the MIL is illuminated when a vehicle receives its AirCare test, the vehicle will fail because it is not operating as it designed.

OBD Test

The On-Board Diagnostic Test, or OBD test, is an emissions test that utilizes a vehicle's built-in On-Board Diagnostic (OBD) System which continuously checks the condition and operation of key emissions control components and emissions-related systems. All 1998 and newer light-duty vehicles come equipped with an OBD system.

If the MIL is on, the test system will download and record the faults stored by the vehicle's OBD system. This information will be printed on your Vehicle Inspection Report and the vehicle will receive a fail result.

If your vehicle's OBD system has completed all of its system checks (no more than one readiness monitor Not Ready) and the MIL is not commanded on, the vehicle will pass the OBD inspection.

For a more detailed description of the OBD test procedure, click here.

OEM

See Original Equipment Manufacturer.

Opacity

Opacity is a measurement, on a percentage scale, of how much light is blocked by the particles in the exhaust plume. Light smoke has a lower opacity than dark smoke. AirCare inspection centres measure the opacity of diesel vehicles using the D147 test procedure. See also Causes of Excess Opacity.

Original Equipment Manufacturer

A general term referring to replacement auto parts made by the same company that manufactured the original part (see also Aftermarket).

Oxidation Catalytic Converter

There are two types of catalytic converters in terms of what their function is: oxidation catalysts oxidize HC and CO. See also Three-Way Catalytic Converter. For more info on trouble-shooting catalytic converters, see Catalytic Converter Testing.

Oxides of Nitrogen (NOx)

Oxides of Nitrogen (NOx) emissions occur when fuels are burned at high temperature. Some of the nitrogen (N2) in the air combines with some of the oxygen (O2) in the air to form nitric oxide (NO). In an engine, some of the NO undergoes additional reactions and turns into nitrogen dioxide (NO2). The emissions of NO and NO2 are collectively referred to as NOx. In addition to contributing to the formation of ozone, NOx emissions also lead to a build up of nitrogen dioxide levels in the atmosphere, which are known to increase the risk of respiratory disease in children. See also Causes of Excess Oxides of Nitrogen.

Oxygen Sensor

A key component in feedback fuel systems is called the Oxygen (O2) Sensor. Located in the exhaust stream, the O2 Sensor detects the relative amount of oxygen that remains after combustion in an engine. The O2 sensor is electrically connected to the on-board computer, which interprets the signal and adjusts the air-fuel ratio as necessary to ensure maximum efficiency. For more info on trouble-shooting oxygen sensors, see Oxygen Sensor Testing.

P

Positive Crankcase Ventilation (PCV)

On all vehicles built since the late 1960s, the Crankcase Vapour Control System prevents crankcase vapours from escaping into the atmosphere. To do this, a regulated amount of vapour is introduced into the engine where it is burned. A key component in regulating this vapour is a PCV Valve or a PCV orifice.

Pollution Control Equipment

See Emissions Control Equipment

Powertrain Control Module (PCM)

All 1998 and newer light-duty vehicles are manufactured with an On-Board Diagnostic (OBD) system that continuously monitors components that affect emission performance. The on-board computer responsible for this is called the Powertrain Control Module or PCM. The PCM is a computer that is designed to control the fuel delivery, ignition, and emission control systems on the engine. The most important function of the on-board computer is to continually adjust the air-fuel ratio so that the engine runs with maximum efficiency (lowest emissions, maximum fuel economy, maximum power, and smoothest idle).

Q

Qualified Waiver

A qualified waiver is a type of conditional pass that occurs because the cause of excess emissions has not been properly identified by an AirCare Certified Repair Centre. As with any conditional pass, this means the vehicle's emission levels will still be higher than they should be, but the vehicle is eligible for licence renewal. However, if the cause of the problem has not been properly identified, you should return to the shop so they can complete the diagnosis.

R

Readiness Monitors

1998 and newer light-duty vehicles have built-in monitoring systems that can detect when emissions control systems have a fault that may cause excess emissions. These monitoring systems perform various checks under certain operating conditions and also give an indication of whether those checks have been performed or not. These indicators are called Readiness Monitors.

If any of the readiness monitors are Not Ready, that means that the system cannot provide a complete picture of the vehicle's emissions control system health. Resolving this situation requires that the vehicle be operated under the circumstances prescribed by the manufacturer that will allow all of the necessary self-diagnostic checks to complete. See your repair centre for more specific information.

If all readiness monitors are set to Ready, that means that the various emissions control systems have been tested and the OBD system can provide a complete picture of the overall emissions control system health.

Repair Cost Limits

To balance emissions compliance requirements with economic considerations, Repair Cost Limits are set out in Section 40.08 of the British Columbia Motor Vehicle Act Regulations. The Repair Cost Limits allow motorists who cannot afford to have expensive repairs completed on their vehicle to re-license the vehicle for up to one year.

A common misconception about Repair Cost Limits is that they represent a minimum amount that must be spent. That is incorrect. As the name implies, the amount is a limit or maximum. The way Repair Cost Limits apply is if the needed emission repairs (as identified by an AirCare Certified Repair Centre) would cost more than the amount specified, the motorist may choose to only authorize partial repairs. The AirCare Certified Repair Centre then completes whatever repairs can be completed without exceeding the Repair Cost Limit, the vehicle is re-inspected, and it receives a conditional pass. The vehicle is then eligible to be re-licensed for up to one year. See also Conditional Pass and Repair Data Form.

Repair Data Form

A report made by AirCare Certified Technicians that describes emissions repairs made to a vehicle that has failed its AirCare inspection. The RDF (may also be referred to as Vehicle Repair Form or VRF) may be a paper copy or it may be in electronic form. The data is submitted to the AirCare Program Administration to ensure that repairs performed are appropriate and effective.

Rich (Air-Fuel Mixture)

A condition where the air-fuel mixture is not the correct ratio (too much fuel relative to the amount of air). High carbon monoxide emissions are a symptom of a rich air fuel mixture.

S

Standards

Typically used in reference to maximum allowable emission limits or cutpoints. Federal emission standards for new vehicles are set by Environment Canada. Provincial standards for in-use vehicles are set by AirCare.

AirCare's maximum allowable emission standards are set to identify vehicles that are emitting significantly higher emissions than a normally operating vehicle of the same age and design. The emission standards are based upon the vehicle's model year, weight and engine size, plus a significant allowance for normal variations in engine performance. A well-tuned vehicle of any model year with its original emission equipment in place and functioning correctly will easily pass the AirCare standards.

Stoichiometric (Air-Fuel Ratio)

When the ratio of air and fuel is precisely correct, it is referred to as stoichiometric. It is critical that air fuel ratio be stoichiometric in order for the mixture to be burned with maximum efficiency and for the catalytic converter to operate with maximum efficiency.

T

Tampering

Removal, disconnection, or mal-adjustment of any aspect of a vehicle's emissions control system is referred to as tampering.

Three-Way Catalytic Converter

There are two types of catalytic converters in terms of what their function is: three-way catalysts (TWC) reduce NOx and oxidize HC and CO. See also Oxidation Catalytic Converter.

Throttle Position Sensor

A throttle is the part on an engine that opens up when the driver steps on the gas pedal. Many fuel-injected engines use a throttle position sensor to determine the driver's demand for power. The measured throttle position is indicated to the vehicle's on-board computer where it is used to calculate how much fuel should be delivered to maintain the desired air-fuel ratio.

U

V

Vacuum Leak

When an engine is running, a vacuum is created in the intake manifold between each of the cylinders in the engine and the throttle. Vacuum Leak refers to leakage in this area. Vacuum leaks can cause disruption of the air-fuel mixture on its way to the cylinders and can result in excessive HC emissions or CO emissions.

W

X

Y

Z