Woodstock Auto Repair

Toll free:(519) 421-2313
Mon - Fri: 8:00 AM - 5:00 PM

Car Care Emission Control System

  1. Air Pump
  2. Catalytic Converter
  3. Check Engine Light
  4. Exhaust Gas Recirculation (EGR)
  5. Filters
  6. Gas Cap
  7. Evaporative System
  8. OBD II
  9. Oxygen Sensor
  10. Vacuum Sensor

Air Pump

Description: Air injection technology first appeared during the late 1960s and was used extensively throughout the 1970s. It was still widely used by some manufacturers through the 1980s, but applications began to fade as automakers developed cleaner-running engines. The typical mechanical air injection system consists of a network of hoses and tubes, a belt-driven air pump and air-management valves.

Since that time, air injection systems have become more diverse in nature, sometimes using the onboard computer to control system operation. Some engines use pulse-air systems that do not use a pump. Instead, alternating pressures in the exhaust stream are used to pull air into the exhaust system. As obsolete as this technology seems, some late-model vehicles use a high-tech air injection system using an electric air pump controlled by the vehicle's Powertrain Control Module (PCM).

Purpose: Essentially an emissions "add-on" installed by the automakers to help further clean up emissions, the air injection system supplies air to the exhaust stream to promote additional burning of exhaust gases such as hydrocarbons (abbreviated as HC) and carbon monoxide (abbreviated as CO). Some systems also supply air to the catalytic converter to further reduce HC, CO and oxides of nitrogen (NOx), a major contributor to photochemical "smog."

Maintenance Tips/Suggestions: Air injection systems require little maintenance, but if your car has one it shouldn't be completely ignored, either. Periodically, the air pump drive belt should be checked to make sure it's in good condition and properly tensioned. Depending on the application, there may be a separate drive belt, or the same belt may drive the pump along with other engine accessories.

To determine if your car has an air injection system, refer to the Vehicle Emission Control Information (VECI) label underneath the hood, which calls out this emissions subsystem if used. Symptoms of problems in the air injection system include a failed emissions test, a broken air pump belt, backfiring through the exhaust, and an overheated/restricted catalytic converter. Electric air pump systems may trigger the CHECK ENGINE or SERVICE ENGINE SOON light when a fault occurs. Proper diagnosis requires accurate insight into system operation, so it's wise to seek a professional technician to pinpoint the exact cause.

Catalytic Converter

Description: Closely resembling a muffler in appearance, the catalytic converter is located in the exhaust system and has an outer shell made of stainless steel. The similarity with a muffler ends there as catalytic converters contain a catalyst made from a noble metal such as platinum, palladium or rhodium. A catalyst is defined as anything that induces or accelerates a change. At least one catalytic converter has been used on cars since 1975; today, cars may have two or more depending on the engine configuration and manufacturer.

Purpose: Using its internal catalyst, a catalytic converter's job is to greatly reduce the level of harmful emissions in a car's exhaust. Namely, these are carbon monoxide, hydrocarbons and oxides of nitrogen. All of these emissions are serious health and environmental hazards, plus they contribute to the formation of photochemical smog. A catalytic converter changes these poisonous gases to harmless carbon dioxide, nitrogen, oxygen, and water. In a simplistic way, the catalytic converter can almost be thought of as an engine of its own. The converter uses fuel and oxygen to "light off" its internal catalyst, which consumes a large portion of the gases flowing through the converter. Although a converter greatly reduces emissions, it does not eliminate them altogether.

Maintenance Tips/Suggestions: Catalytic converters do not require maintenance of their own, but their long-term livelihood depends on proper care and maintenance of your vehicle. As an example, if your vehicle begins to run rough, produces smoke from the tailpipe, or the SERVICE ENGINE SOON or CHECK ENGINE light appears, have it checked out immediately by a professional technician. This is especially true if the SERVICE ENGINE SOON or CHECK ENGINE flashes rather than being steadily lit. Neglecting these warning signs can cause expensive damage to the converter, requiring replacement. Symptoms of a faulty or failing converter may include failing an emissions test, poor performance, increased engine temperature, and bucking or hesitation.

Check Engine Light

Description: An orange indicator light labelled CHECK ENGINE or SERVICE ENGINE SOON, it's also known as the MIL (Malfunction Indicator Lamp) in technical jargon. The importance and function of this light became more critical starting in 1996, when the second generation of onboard diagnostics, known as OBDII, became standard equipment on all makes and models of cars.

Purpose: Required by for tighter emissions control, OBDII has the ability to monitor a diverse range of engine-related functions and record critical information. You can think of this information as your car's electronic "vital signs". OBDII information has proven to be so credible that it is now being used by some jurisdictions in the United States and around the world as part of their emissions testing programs. The SERVICE ENGINE SOON or CHECK ENGINE LIGHT has several modes and can indicate a normally functioning system, a system that requires prompt attention, and a system that needs immediate attention.

Maintenance Tips/Suggestions: If your car's OBDII system is functioning properly, the CHECK ENGINE or SERVICE ENGINE SOON light should flash briefly when you turn your car's ignition key to the on position. After the brief flash, the light should go out and remain off while you are driving.

A glowing CHECK ENGINE or SERVICE ENGINE SOON light alerts you to problems in your car's onboard diagnostic system that should be checked out as soon as possible. There's no reason to panic and in many cases, you won't notice any difference in vehicle performance.

First, check the gas cap to make sure it wasn't left loose after refuelling. Sometimes, this can trigger the light. Most OBDII-equipped vehicles have a gas cap that simply snaps in place, when turned to the right. Some early OBDII-equipped vehicles have threaded caps. On these, just turn the cap to the right until it begins to click. If the gas cap was loose, the light should go out after a few short trips.

If the gas cap wasn't the problem and the light remains on steady, have the system checked out as soon as possible. A light that flashes requires more prompt attention, indicating a more severe condition that must be checked out immediately to prevent damage to the catalytic converter. When you experience a flashing light, minimize driving at high speeds or under heavy loads. When scheduling service, make sure the shop that diagnoses your car has technicians who are properly trained and certified for OBDII diagnosis and repair.

Exhaust Gas Recirculation (EGR)

Description: The Exhaust Gas Recirculation (EGR) valve and its related components first appeared on automobiles in 1972. The valve may be controlled by vacuum or electronically depending on the year, make and manufacturer of the vehicle. The use of EGR is on the decline since manufacturers began to use fuel injection, which provides more accurate control over the fuel and air mixture.

Purpose: EGR systems help reduce the level of harmful oxides of nitrogen emissions (NOx) in the exhaust. This type of emission increases with combustion temperature. Although at first impression it may appear counter-productive, the EGR system does this by introducing calibrated amounts of exhaust gas into the engine's intake system. Since the exhaust gas-for the most part-doesn't burn, it takes up some of the space in the combustion chamber of the air/fuel mixture. As a result, combustion chamber temperature drops and so do NOx emissions.

Maintenance Tips/Suggestions: EGR systems usually do not require regular maintenance. Signs of a malfunctioning EGR valve or its related components include engine spark knock under acceleration, rough idle, stalling, and reduced power. To determine if your car has an EGR system, refer to the Vehicle Emission Control Information (VECI) label underneath the hood, which will call out this emissions subsystem if so equipped. If you suspect a problem with your vehicle's EGR system, have it checked out by a professional technician. A malfunctioning system, if neglected long enough, can cause engine damage.

Emission Testing Program

Description: A program designed to periodically check vehicle emissions to ensure they are within limits. Often referred to as an I/M (Inspection/Maintenance) program, they are used in numerous provinces to improve air quality in those areas.

The type of program varies in each province that has a system (British Columbia and Ontario; Quebec has one for Heavy duty Vehicles), there are variances with other jurisdictions such as states in the United States as well. There are differences in the type of test used, vehicle populations to be tested and other program-specific details. There are centralized programs that have province-contracted test stations exclusively dedicated to testing. Other jurisdictions run decentralized programs, where emissions can be tested at local repair facilities. In a few cases, jurisdictions may run "hybrid" programs using both centralized and decentralized test stations. The latest trend is to incorporate the use of second-generation onboard diagnostics (OBDII) into these programs, in many cases altogether eliminating the need for tailpipe emissions tests.

Purpose: I/M programs evaluate the emissions from vehicles and single out those that are polluting beyond the limits established for certain model years of vehicles. Aside from identifying vehicles with high emissions, such programs advocate proper maintenance to prevent high emissions due to maintenance neglect.

Maintenance Tips/Suggestions: The best way to keep your vehicle environmentally friendly is by performing regularly scheduled maintenance, rather than waiting to correct a problem after your car fails an emissions test. If the SERVICE ENGINE SOON or CHECK ENGINE light appears, have it checked out immediately by a professional technician. Neglecting these warning signs can cause lead to more extensive and expensive repairs.


Description: Oil filter, air filter, crankcase breather filter, fuel filter, canister filter.

Purpose: The oil filter traps harmful debris from being recirculated back through the engine's lubrication system. The air filter stops harmful dirt particles from entering the engine's air intake system where they may cause engine damage. The crankcase breather filter cleans the air pulled into the engine crankcase by the Positive Crankcase Ventilation (PCV) system or a metered orifice. The fuel filter cleans the fuel before it reaches the fuel delivery system, namely the fuel injectors. The canister filter cleans the air entering the carbon canister, part of the emissions system.

Maintenance Tips/Suggestions: Always replace filters at the scheduled maintenance interval, but more often if your driving conditions require it. Neglecting filter changes can result in poor performance, engine damage or a breakdown.

Gas Cap

Description: The gas cap consists of a plastic body with either threads (older caps) or lugs that locates into the filler neck of the fuel tank. Quality caps incorporate finely calibrated springs and valves. Caps may come in standard or locking types that minimize the chances of tampering with the fuel tank.

Purpose: The gas cap used to simply cover the opening of the fuel tank filler neck, but eventually strong safety and emissions initiatives pushed cap designs to accomplish other tasks. The gas cap is now a major safety component that prevents the flow of fuel back out of the tank filler when a car is in an accident, including rollovers. This helps to reduce the chances of fuel leaks and their associated dangers. The gas cap is also an integral part of the onboard diagnostics system (OBDII) and emissions control system, which are interrelated.

The cap prevents the leakage of fuel vapours from the filler neck, which can be a major source of hydrocarbon emissions. A leaking or missing gas cap can result in the release of 90 litres of fuel per year into the atmosphere.

Maintenance Tips/Suggestions: Always make sure your car's gas cap is reinstalled properly after each fill-up. If you lose the cap, replace it immediately for safety and emissions reasons. A loose gas cap can cause your car's SERVICE ENGINE SOON or CHECK ENGINE light to come on. If you find the cap loose, turn it to the right until it "snaps". It may take several start-and-run cycles for the light to reset. In areas with an emissions testing program, the gas cap may be tested for its ability to hold pressure. If the cap fails, it will need to be replaced. When you replace your car's gas cap, make sure it's made by a reliable manufacturer and that it's the right cap for that specific make and model. Beware of "one size fits all" caps and low-quality alternatives that may jeopardize your safety and your car's emissions control system.

Evaporative System

Description: The evaporative system, sometimes abbreviated as EVAP, consists of the fuel cap, fuel tank, carbon canister, canister purge valve, interconnecting lines and hoses.

Purpose: Contains fuel vapours (hydrocarbons) instead of releasing them into the atmosphere and stores them in a carbon canister. The collected vapours are then routed to the engine where they can be burned. Since evaporative emissions can be a major contributor of pollution from automobiles, a system check is part of an emissions test under an emissions testing program.

Maintenance Tips/Suggestions: The main service item of the evaporative system is the carbon canister filter, if equipped. Check your owner's manual for specifics on replacing this filter. Beyond that, regular engine performance checks should be all that's required to ensure proper operation of the evaporative system. A failure in this system could trigger the SERVICE ENGINE SOON or CHECK ENGINE light. If the light appears, have its cause investigated by a professional technician as soon as possible.
In areas with an emissions testing program, the gas cap is tested for its ability to hold pressure. If the cap fails, it will need to be replaced in order to pass the test.


Description: Second-generation onboard diagnostics, more commonly known as OBDII, is a sophisticated onboard computer system that was first used on some 1994 and 1995 model vehicles. Since 1996, it is used on all makes and models and cars and light trucks. OBDII uses a network of sensors to monitor operating conditions.

Purpose: Government agencies mandated the application of OBDII technology to keep tighter reins on vehicle emissions. In addition, OBDII brings about certain standards intended to help streamline the diagnostic process, regardless of the make of vehicle. The system also alerts you with a Malfunction Indicator Lamp (MIL), indicating that the system has detected a problem, which could cause excessive emissions. This light is usually labelled SERVICE ENGINE SOON or CHECK ENGINE. If the light appears, you should have its cause investigated by a professional technician at your earliest opportunity. If the light flashes, the condition is more severe and must be checked out immediately to prevent damage to the catalytic converter.

Maintenance Tips/Suggestions: Perform routine maintenance as recommended in your owner's manual. The onboard computer, otherwise know as the powertrain control module, stores a Diagnostic Trouble Code (DTC) when it detects a problem in one of the monitored circuits. A professional technician can access this information using a scan tool connected to the vehicle's Data Link Connector (DLC). Although many DTCs are sensor-related, it does not necessarily indicate a faulty sensor. There may be problems in that sensor's circuit, or there may be several interrelated problems. Areas of the country with an emissions testing program are placing added value on OBDII checks, where this technology may be used in place of tailpipe testing.

Oxygen Sensor

Description: Located in the exhaust system at one or more points, an oxygen sensor converts the status of the engine's air/fuel mixture into a corresponding voltage signal. The oxygen sensor is sometimes referred to as a Lambda sensor on some European cars.

The most common type of sensor uses a zirconia element to generate voltage. Titania oxygen sensors, on the other hand, use the technology of electrical resistance to produce similar voltage characteristics as zirconia sensors. Regardless of the technology used, changes in the air/fuel mixture result in a voltage change that is monitored by the vehicle's powertrain control module. Many oxygen sensors also have built-in heaters, to warm them to operating temperature more quickly. Prior to 1996, most cars had one oxygen sensor. In 1996, Onboard Diagnostics II (OBDII) became standard technology for all makes and models. OBD II systems use one oxygen sensor on the inlet to the catalytic converter and another one on the outlet. On cars with dual converters, there may be as many as four oxygen sensors.

Purpose: The oxygen sensor reports live information about the engine's air/fuel mixture to the powertrain control module. This information is used primarily to help calculate fuel delivery to the engine, which changes continuously while it is running. If the engine is running lean, the powertrain control module will sense this from the oxygen sensor's signal and increase the air/fuel mixture to the engine. Conversely, just the opposite occurs when the engine begins to run rich. On OBDII-equipped vehicles, the sensors are also used to help determine the efficiency of the catalytic converter. The powertrain control module does this by comparing the signal of the sensor located at the inlet of the catalytic converter with the signal of the sensor located at the outlet of the converter.

Maintenance Tips/Suggestions: Replace at the interval as recommended in the owner's manual or when other conditions dictate, such as failing an emissions test. Some cars have an oxygen sensor light that appears when oxygen sensor replacement is needed. Some symptoms of a faulty oxygen sensor include poor gas mileage, a failed emissions test, "rotten-eggs" smell from the exhaust, poor acceleration and more. Although a faulty oxygen sensor can cause the SERVICE ENGINE SOON or CHECK ENGINE light to appear, it's best to have the cause checked out immediately by a professional technician. This is especially true if the SERVICE ENGINE SOON or CHECK ENGINE light flashes rather than staying on steady. Neglecting these warning signs can cause expensive damage to the catalytic converter, requiring replacement.

Vacuum Sensor

Description: The vacuum system consists of a network of hoses, lines and valves that connect vacuum-operated devices to the engine.

Purpose: Despite the growing use of electronics on today's cars, automakers continue to use a power source created by the "breathing" of the engine vacuum. It can be used to operate the power brake booster, cruise control or even as a signal of engine load.

Maintenance Tips/Suggestions: Vacuum hoses and lines require regular inspection to make sure they're in good condition and secure. Because of the extreme heat under the hood in your vehicle, it can cause hoses to break down, sometimes causing leaks or they may even collapse, preventing vacuum from getting to its intended part. Also, fuel vapours present in your vehicle's fuel and air intake system can attack hoses making them weak. Symptoms of vacuum problems may be high idle speed, bucking and surging, overall poor engine performance, excessive fuel consumption, a "hard" brake pedal, or a hissing sound from underneath the hood. Always replace any bad lines or hoses.