here is the info
how the emissions are formed:
Car emissions are biproducts of the internal combustion engine of a car, which is released into the atmosphere via the car's exhaust system. These emissions are significant contributors to air pollution and also form the main ingredients required to create smog in many of the larger cities around the world. In this respect, emissions are of importance as they have been found to have many detrimental effects on both public health and the environment.
Hydrocarbons are toxins which form the main ingredient in smog (see also ‘Smog' section). They are formed when fuel is burned in the car and are can be described as burned or partially burned fuel
Carbon Monoxide (CO) is an odourless, colourless and tasteless gas which is highly toxic to humans. It is responsible for the majority of fatal air poisoning incidents in developed countries, In cars, carbon monoxide is produced as a result of incomplete combustion of the fuel.
Mono-nitrogen oxides can be either nitrogen oxide (NO) or nitrogen dioxide (NO2). Consequently, they are often generically referred to as "NOx" pollutants (effectively,
NOx is a mixture of NO and NO2).
They are generated when nitrogen in the air reacts with oxygen under the conditions of high temperature and pressure in the engine. NOx is a precursor to smog and acid rain. NO and NO2 react with water, ammonia and a number of other compounds to form (amongst other nasties), nitric acid vapour.
Nitric acid vapour can penetrate deep into lung tissue and damage it
Generally the emission of Carbon dioxide from a car is considered a "best case scenario" (it means that fuel is being burned effectively), it is still a greenhouse gas.
Motor vehicle Carbon Dioxide emissions form a significant part of the man made contribution to the growth of Carbon dioxide concentrations in the atmosphere which is believed by a majority of scientists to play a significant part in climate change
A photochemical smog is the chemical reaction of sunlight, nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the atmosphere, which leaves airborne particles (called particulate matter) and ground-level ozone.
Nitrogen oxides are released by nitrogen and oxygen in the air reacting together under high temperature and pressure of the car engine (as well as industrial manufacturing factories). VOCs are released from man-made sources such as gasoline (petrol) as well as paint, solvents and pesticides
how theirements emission(s) are controlled:
The need to control car emissions, such as hydrocarbons, NOx and carbon monoxide, has lead to the development of a number of pollution control devices in the car. The desire to reduce emissions has also, over the course of time, necessitated the computerisation of the car.
In 1981, the first of a series of advancements as a "self adjusting engine" which featured a feedback control system. This consisted of an oxygen sensor fitted on the exhaust system, which would measure the oxygen content of the emissions. It would then send a signal back to a computer which would analyse the oxygen value and adjust the air / fuel mix accordingly.
As the onboard computer systems advanced, they were also able to adjust things like ignition spark timing and control other emission monitoring systems on the vehicle. Now, computer systems are so advanced that they are capable of self - diagnosing, alerting the driver to any outages with a warning light on the dash. At the same time, the computer logs the issue internally with other diagnostic information which can later be examined by a technician.
Generally, emissions are controlled in three ways:
1. To promote more complete combustion in the engine, so there are generally less bi products such as carbon monoxide and hydrocarbons to be emitted.
2. To reintroduce hydrocarbons back into the engine and give the a "second chance" of complete combustion and conversion into less harmful compounds
3. To provide an additional area for combustion to take place (this is how catalytic converters function).
Explain how the system/components are tested:
The electronic emissions control unit or computer monitors
certain powertrain functions and controls various operating parameters
to help the vehicle run efficiently and with the lowest possible
emissions. Ignition, transmission function, air injection, exhaust
gas recirculation (EGR), engine operating temperature and fuel system
parameters are some of the systems monitored and/or controlled by the
electronic emissions control unit car computer .
The onboard emissions diagnostic device monitors the operation of
a vehicle's emission control system and alerts the driver with a
dashboard light when malfunctions occur. The system will record where
the problem is occurring and assist automotive technicians in
diagnosing and repairing emission control malfunctions. Since some
emission control malfunctions do not have an adverse effect on vehicle
performance, they can go undetected by the driver for quite some time.
The onboard diagnostic device will help catch malfunctions early,
preventing a significant output of harmful exhaust emissions from your
vehicle, and possibly in time to be covered by the emissions control
warranty. Often this "device" is part of the electronic control unit
EMISSION CONTROL PARTS
Exhaust Gas Conversion Systems
oxygen sensor thermal reactor
catalytic converter dual-walled exhaust pipe
Exhaust Gas Recirculation System
EGR valve thermal vacuum switch
EGR solenoid EGR spacer plate
EGR backpressure transducer Sensor and switches use to
control EGR flow
Evaporative Emission Control System
purge valve fuel filler cap
purge solenoid vapor storage canister and filter
Positive Crankcase Ventilation (PCV) System
PCV valve PCV solenoid
Air Injection System
Air pump diverter, bypass, or gulp valve
reed valve anti-backfire or deceleration valve
Early Fuel Evaporative (EFE) System
EFE valve thermal vacuum switch
heat riser valve
Fuel Metering System
electronic control module (unit) or EFI air flow meter, computer
command module or mixture control unit, deceleration controls,
electronic choke, fuel injectors, fuel injection units and fuel
altitude compensator sensor, bars or rails for EFI or TBI systems,
mixture settings on sealed fuel mixture control solenoid, diaphragm
or other systems, fuel metering components that achieve closed/other
feedback control sensors/loop operation switches and valves
Air Induction System
thermostatically controlled air cleaner, air box
electronic spark advance timing advance/retard systems,
high energy electronic ignition
hoses, gaskets, brackets, clamps and other accessories used in the
EMISSION RELATED PARTS
These are examples of other parts of your vehicle which have a
primary purpose other than emissions control but which nevertheless
have significant effects on your vehicle's emissions. If any of these
parts fail to function or function improperly, your vehicle's
emissions may exceed federal standards. Therefore, when any of the
parts of the following systems are defective in materials or
workmanship and have failed in a way that would be likely to cause
your vehicle's emissions to exceed federal standards, they should be
repaired or replaced under the emissions warranty:
Describe the symptoms resulting from faulty system components (what will the customer complain about?)Describe any servicing requ
faulty system when emisson are not controlled dash warrning light will turn on and that is sign the emission are out of control to test the part system has obd2 diagnositc
and early 1980's manufacturers started using electronic means to control engine functions and diagnose engine problems. This was primarily to meet EPA emission standards. Through the years on-board diagnostic systems have become more sophisticated. OBD-II, a new standard introduced in the mid-'90s, provides almost complete engine control and also monitors parts of the chassis, body and accessory devices, as well as the diagnostic control network of the car.
The service industry calls the Check Engine light on your dash an "MIL" or Malfunction Indicator Light. It shows three different types of signals. Occasional flashes show momentary malfunctions. It stays on if the problem is of a more serious nature, affecting the emissions output or safety of the vehicle. A constantly flashing MIL is a sign of a major problem which can cause serious damage if the engine is not stopped immediately. In all cases a "freeze frame" of all sensor readings at the time is recorded in the central computer of the vehicle.
Hard failure signals caused by serious problems will cause the MIL to stay on any time the car is running until the problem is repaired and the MIL reset. Intermittent failures cause the MIL to light momentarily and they often go out before the problem is located. The freeze frame of the car's condition captured in the computer at the time of the malfunction can be very valuable in diagnosing these intermittent problems. However, in some cases if the car completes three driving cycles without a re-occurrence of the problem, the freeze frame will be erased.
service repair after the system indicated the failed part like oxygen sensor or catalytic converter you test with scanner and read output radings and repalce parts as needed