Description: Sensors measure a variety of operating parameters that help to reduce emissions and also serve functions for the engine, transmission and other systems. These sensors generally include the manifold air temperature sensor, coolant temperature sensor, manifold absolute pressure sensor (MAP Sensor), mass airflow sensor (MAF Sensor), throttle position sensor, vehicle speed sensor and oxygen sensors.
Purpose: All of these sensors provide critical operating information to the vehicle’s powertrain control module, the onboard computer that compares the signals from the sensors to programmed values. Based on the signals, the computer then issues commands to various output devices to control the engine and transmission, along with reducing emissions. 1996 and newer vehicles are equipped with second-generation onboard diagnostics (OBDII) systems that put special emphasis on sensor values and emissions.
Maintenance Tips/Suggestions: Sensors do not require regular maintenance or adjustments. Regardless of what a specific sensor measures, all operate within a range of normal values. If a sensor provides a signal outside the normal range long enough, the powertrain control module will set a trouble code, which will usually trigger the SERVICE ENGINE SOON or CHECK ENGINE light.
Check Engine Light
Description: An orange indicator light labeled 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
First, check the gas cap to make sure it wasn’t left loose after refueling. 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.
Description: The crankcase ventilation system, often called positive crankcase ventilation (PCV), consists of a PCV valve or metered orifice (calibrated opening), its vacuum hose or line, a supply hose providing air into the crankcase, and on some applications, a breather filter to clean the air provided to the supply hose.
Purpose: The purpose of the PCV valve is to regulate the flow of crankcase fumes into the intake manifold where they can be burned. Prior to 1963, cars had no PCV and used road draft tubes that just left the hydrocarbon emissions from the crankcase out into the open air. The PCV valve also has a secondary role as a check valve, to prevent flow back into the crankcase. This prevents potential ignition of the crankcase fumes, should the engine backfire. The PCV system is also crucial for to proper engine sealing. The system alleviates crankcase pressure, which can push out on seals and gaskets, contributing to oil leaks.
Maintenance Tips/Suggestions: Often times, the PCV system gets completely overlooked during routine maintenance. This is unfortunate, because PCV faults often mimic problems in other areas. Check your owner’s manual for PCV maintenance intervals and replace the valve as recommended. Oil leaks are one clue of a faulty PCV system. Leaking valve cover gaskets and rear main seals are but a few examples. If the PCV system isn’t operating correctly, crankcase pressure can build and force oil past gaskets and seals that would have otherwise been OK.
Drivability problems can also result from the PCV system. Hesitation and surging can occur if the wrong valve is used or there’s a leak in the PCV vacuum hose.
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.
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.
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: A failure in this system could trigger the SERVICE ENGINE SOON or CHECK ENGINE light. 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.
OBD II (On-Board Diagnostics, Second Generation)
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 mandatory on all makes and models of cars and light trucks built for use in North America. 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 labeled SERVICE ENGINE SOON or CHECK ENGINE. 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.
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. 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. 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.
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 rubber and plastic 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.
Description: Ignition components generally include spark plugs, ignition wires, distributor cap, distributor rotor, distributor, ignition coil, ignition module and primary circuit triggering device. For ignition management, the system also relies on the powertrain control module (PCM), which also manages other engine functions. The names and exact use of ignition components varies widely among different makes and models. For example, many ignition systems no longer use a distributor and consequently do not have any of its related parts.
Purpose: As a team, the ignition components work together to sense engine position and conditions and provide a high-energy spark inside the engine’s cylinders at precisely the right instant.
Maintenance Tips/Suggestions: Refer to your owner’s manual for recommended service intervals for the ignition system. An engine that runs rough, bucks, surges, stalls, gets poor fuel economy or fails an emissions test are all signs of a potential ignition system problem. Although some cars now use platinum spark plugs with 100,000-kilometre service life, other parts such as ignition wires still need attention and periodic replacement. If your car exhibits any symptoms such as those mentioned here, you may also experience a glowing CHECK ENGINE OR SERVICE ENGINE SOON light on the dash. A flashing check engine light is indicating that the PCM has detected a misfire condition. Misfire is when a cylinder fails to burn fuel adequately enough to power the engine similar to the other firing cylinders.
Description: The typical spark plug consists of an outer shell, a connecting terminal, a core, a seat area, a centre electrode, and one or more ground electrodes. Spark plugs used steel/nickel electrodes traditionally, but newer plug designs use electrodes made of precious metals such as platinum or even gold/palladium alloy. These types of electrode materials are much less susceptible to erosion, provide longer life and tend to resist fouling better than their predecessors. Most engines use one spark plug per cylinder, although some engines use two. Spark plugs come in different configurations, such as different threads, seats, “reach lengths”, and heat ranges.
Purpose: The spark plug ignites the air/fuel mixture inside the cylinder. This occurs when high voltage, triggered at precisely the right instant, bridges the gap between the centre and the ground electrodes. The end result is an even burning of the air/fuel mixture inside the cylinder. The spark plug also provides a secondary purpose of helping to channel some heat away from the cylinder.
Maintenance Tips/Suggestions: Typical replacement intervals range between 50,000 and 100,000 kilometers, depending on the vehicle and the type of spark plug. Always consult your owner’s manual for your specific vehicle. Symptoms of one or more faulty spark plugs include poor gas mileage, a failed emissions test, and rough running/poor acceleration with the engine under load.