OBJECTIVES After studying Chapter 37, the reader will be able to:

OBJECTIVES After studying Chapter 37, the reader will be able to:
Prepare for the ASE Engine Performance (A8) certification test content area “D” (Emission Control Systems). Describe the purpose and function of the exhaust gas recirculation system. Explain methods for diagnosing and testing for faults in the exhaust gas recirculation system. Describe the purpose and function of the positive crankcase ventilation and the air injection reaction system. Explain methods for diagnosing and testing faults in the PCV and AIR systems.

OBJECTIVES Describe the purpose and function of the catalytic converter. Explain the method for diagnosing and testing the catalytic converter. Describe the purpose and function of the evaporative emission control system. Discuss how the evaporative emission control system is tested under OBD-II regulations. Explain methods for diagnosing and testing faults in the evaporative emission control system.

SMOG The common term used to describe air pollution is smog, a word that combines the two words smoke and fog. Smog is formed in the atmosphere when sunlight combines with unburned fuel (hydrocarbon, or HC) and oxides of nitrogen (NOX) produced during the combustion process inside the cylinders of an engine. Smog is ground-level ozone (O3), a strong irritant to the lungs and eyes. HC (unburned hydrocarbons). CO (carbon monoxide). NOX (oxides of nitrogen).

SMOG FIGURE 37-1 Notice the haze caused by nitrogen oxides that is often over many major cities.

EXHAUST GAS RECIRCULATION SYSTEMS
Exhaust gas recirculation (EGR) is an emission control that lowers the amount of nitrogen oxides (NOX) formed during combustion.

EXHAUST GAS RECIRCULATION SYSTEMS NOx Formation
Nitrogen N2 and oxygen O2 molecules are separated into individual atoms of nitrogen and oxygen during the combustion process. These then bond to form NOX (NO, NO2). When combustion flame front temperatures exceed 2,500°F (1,370°C), NOX formation increases dramatically.

EXHAUST GAS RECIRCULATION SYSTEMS Controlling NOX
The amounts of NOX formed at temperatures below 2,500°F (1,370°C) can be controlled in the exhaust by a catalyst. To handle the amounts generated above 2,500°F (1,370°C), the following are some methods that have been used to lower NOX formation: Enrich the air–fuel mixture. Lower the compression ratio. Dilute the air–fuel mixture.

FIGURE 37-2 When the EGR valve opens, exhaust gases flow through the valve and into passages in the intake manifold.

FIGURE 37-3 A vacuum-operated EGR valve. The vacuum to the EGR valve is computer controlled by the EGR valve control solenoid.

EXHAUST GAS RECIRCULATION SYSTEMS EGR System Operation
Since small amounts of exhaust are all that is needed to lower peak combustion temperatures, the orifice that the exhaust passes through is small.

EXHAUST GAS RECIRCULATION SYSTEMS EGR System Operation
Because combustion temperatures are low, EGR is usually not required during the following conditions: Idle speed When the engine is cold At wide-open throttle (WOT)

EXHAUST GAS RECIRCULATION SYSTEMS Positive and Negative Backpressure EGR Valves
Some EGR valves used on older engines are designed with a small valve inside that bleeds off any applied vacuum and prevents the valve from opening. These types of EGR valves require a positive backpressure in the exhaust system. This is called a positive backpressure EGR valve.

EXHAUST GAS RECIRCULATION SYSTEMS Positive and Negative Backpressure EGR Valves
Behind each pulse is a small area of low pressure. Some EGR valves react to this low pressure area by closing a small internal valve, which allows the EGR valve to be opened by vacuum. This type of EGR valve is called a negative backpressure EGR valve.

EXHAUST GAS RECIRCULATION SYSTEMS Computer-Controlled EGR Systems
The computer controls a solenoid to shut off vacuum to the EGR valve at cold engine temperatures, idle speed, and wide-open throttle operation. If two solenoids are used, one acts as an off/on control of supply vacuum, while the second solenoid vents vacuum when EGR flow is not desired or needs to be reduced.

EXHAUST GAS RECIRCULATION SYSTEMS EGR Valve Position Sensors
Late-model, computer-controlled EGR systems use a sensor to indicate EGR operation. On-board diagnostics generation-II (OBD-II) EGR system monitors require an EGR sensor to do their job.

FIND THE ROOT CAUSE FIGURE 37-4 An EGR valve position sensor on top of an EGR valve.

COMPUTER-CONTROLLED EGR SYSTEMS Digital EGR Valves
GM introduced a completely electronic, digital EGR valve design on some 1990 engines. The digital EGR valve consists of three solenoids controlled by the PCM.

COMPUTER-CONTROLLED EGR SYSTEMS Linear EGR
Most General Motors and many other vehicles use a linear EGR that contains a solenoid to precisely regulate exhaust gas flow and a feedback potentiometer that signals the computer regarding the actual position of the valve. FIGURE 37-5 A General Motors linear EGR valve.

COMPUTER-CONTROLLED EGR SYSTEMS Linear EGR
FIGURE 37-6 The EGR valve pintle is pulse-width modulated and a three-wire potentiometer provides pintle-position information back to the PCM.

OBD-II EGR MONITORING STRATEGIES
In 1996, the U.S. EPA began requiring OBD-II systems in all passenger cars and most light-duty trucks. These systems include emissions system monitors that alert the driver and the technician if an emissions system is malfunctioning.

FIGURE 37-7 A DPFE sensor and related components.

FIGURE 37-8 An OBD-II active test. The PCM opens the EGR valve and then monitors the MAP sensor and/or engine speed (RPM) to meet acceptable values.

DIAGNOSING A DEFECTIVE EGR SYSTEM
If the EGR valve is not opening or the flow of the exhaust gas is restricted, then the following symptoms are likely: Ping (spark knock or detonation) during acceleration or during cruise (steady-speed driving) Excessive oxides of nitrogen (NOX) exhaust emissions If the EGR valve is stuck open or partially open, then the following symptoms are likely: Rough idle or frequent stalling Poor performance/low power, especially at low engine speed

THE SNAKE TRICK FIGURE 37-9 Removing the EGR passage plugs from the intake manifold on a Honda.

DIAGNOSING A DEFECTIVE EGR SYSTEM

CRANKCASE VENTILATION
The problem of crankcase ventilation has existed since the beginning of the automobile, because no piston ring, new or old, can provide a perfect seal between the piston and the cylinder wall.

CRANKCASE VENTILATION
FIGURE A PCV valve shown in a cutaway valve cover showing the baffles that prevent liquid oil from being drawn into the intake manifold.

PCV VALVES The PCV valve in most systems is a one-way valve containing a spring-operated plunger that controls valve flow rate. FIGURE Spring force, crankcase pressure, and intake manifold vacuum work together to regulate the flow rate through the PCV valve.

PCV VALVES FIGURE Air flows through the PCV valve during idle, cruising, and light-load conditions. FIGURE Air flows through the PCV valve during acceleration and when the engine is under a heavy load.

PCV VALVES FIGURE PCV valve operation in the event of a backfire.

ORIFICE-CONTROLLED SYSTEMS
The closed PCV system used on some 4-cylinder engines contains a calibrated orifice instead of a PCV valve. While most orifice flow control systems work the same as a PCV valve system, they may not use fresh air scavenging of the crankcase. Crankcase vapors are drawn into the intake manifold in calibrated amounts depending on manifold pressure and the orifice size.

ORIFICE-CONTROLLED SYSTEMS Separator Systems
Turbocharged and many fuel-injected engines use an oil/vapor or oil/water separator and a calibrated orifice instead of a PCV valve.

(PCV) SYSTEM DIAGNOSIS
When intake air flows freely, the PCV system functions properly, as long as the PCV valve or orifice is not clogged. Modern engine design includes the air and vapor flow as a calibrated part of the air–fuel mixture. PCV System Performance Check The Rattle Test The 3x5 Card Test The Snap Back Test Crankcase Vacuum Test

(PCV) SYSTEM DIAGNOSIS
FIGURE Using a gauge that measures vacuum in units of inches of water to test the vacuum at the dipstick tube, being sure that the PCV system is capable of drawing a vacuum on the crankcase (28 inches of water equals 1 PSI or about 2 in.Hg of vacuum).

PCV MONITOR The PCV monitor will fail if the PCM detects an opening between the crankcase and the PCV valve or between the PCV valve and the intake manifold.

PCV MONITOR FIGURE Most PCV valves used on newer vehicles are secured with fasteners, which makes it more difficult to disconnect and thereby less likely to increase emissions.

SECONDARY AIR INJECTION SYSTEM
An air pump provides the air necessary for the oxidizing process inside the catalytic converter. FIGURE A typical belt driven air pump. Air enters through the revolving fins. These fins act as a moving air filter because dirt is heavier than air, and therefore the dirt in the air is deflected off the fins at the same time the air is drawn into the pump.

SECONDARY AIR INJECTION SYSTEM
FIGURE (a) When the engine is cold and before the oxygen sensor is hot enough to reach closed loop, the air flow is directed to the exhaust manifold(s) through one-way check valve(s). These valves keep exhaust gases from entering the switching solenoids and the air pump itself. (b) When the engine achieves closed loop, the air flows through the pump, is directed to the catalytic converter, and then moves through a check valve.

AIR DISTRIBUTION MANIFOLDS AND NOZZLES
The air-injection system sends air from the pump to a nozzle installed near each exhaust port in the cylinder head. This provides equal air injection for the exhaust from each cylinder and makes it available at a point in the system where exhaust gases are the hottest.

Air is delivered to the exhaust system in one of two ways: An external air manifold, or manifolds, distributes the air through injection tubes with stainless steel nozzles. The nozzles are threaded into the cylinder heads or exhaust manifolds close to each exhaust valve. An internal air manifold distributes the air to the exhaust ports near each exhaust valve through passages cast in the cylinder head or the exhaust manifold. Exhaust Check Valves Belt-Driven Air Pumps Electric Motor-Driven Air Pumps

FIGURE A typical electric motor-driven AIR pump. This unit is on a Chevrolet Corvette and only works when the engine is cold.

SECONDARY AIR INJECTION SYSTEM DIAGNOSIS
The air pump system should be inspected if an exhaust emissions test failure occurs. In severe cases, the exhaust will enter the air cleaner assembly, resulting in a horribly running engine because the extra exhaust displaces the oxygen needed for proper combustion.

SECONDARY AIR INJECTION SYSTEM DIAGNOSIS Visual Inspection
Carefully inspect all air injection reaction (AIR) system hoses and pipes. Any pipes that have holes and leak air or exhaust require replacement.

SECONDARY AIR INJECTION SYSTEM DIAGNOSIS Four-Gas Exhaust Analysis
An SAI system can be easily tested using an exhaust gas analyzer. Follow these steps: Start the engine and allow it to run until normal operating temperature is achieved. Connect the analyzer probe to the tailpipe and observe the exhaust readings for hydrocarbons (HC) and carbon monoxide (CO). Using the appropriate pinch-off pliers, shut off the air flow from the AIR system. Observe the HC and CO readings. Record the O2 reading with the AIR system still inoperative. Unclamp the pliers and watch the O2 readings.

CATALYTIC CONVERTERS A catalytic converter is an aftertreatment device used to reduce exhaust emissions outside of the engine. This device is installed in the exhaust system between the exhaust manifold and the muffler, and usually is positioned beneath the passenger compartment. FIGURE Most catalytic converters are located as close to the exhaust manifold as possible as seen in this display of a Chevrolet Corvette.

CERAMIC MONOLITH CATALYTIC CONVERTER
Most catalytic converters are constructed of a ceramic material in a honeycomb shape with square openings for the exhaust gases. The substrate is contained within a round or oval shell made by welding together two stamped pieces of aluminum or stainless steel. FIGURE A typical catalytic converter with a monolithic substrate.

CERAMIC MONOLITH CATALYTIC CONVERTER Catalytic Converter Operation
The converter contains small amounts of rhodium, palladium, and platinum. These elements act as catalysts. A catalyst is an element that starts a chemical reaction without becoming a part of, or being consumed in, the process. In a three-way catalytic converter (TWC) all three exhaust emissions (NOx, HC, and CO) are converted to carbon dioxide (CO2) and water (H2O).

CERAMIC MONOLITH CATALYTIC CONVERTER Catalytic Converter Operation
FIGURE The three-way catalytic converter first separates the NOX into nitrogen and oxygen and then converts the HC and CO into harmless water (H2O) and carbon dioxide (CO2).

CERAMIC MONOLITH CATALYTIC CONVERTER Converter Light-Off
The catalytic converter does not work when cold and it must be heated to its light-off temperature of close to 500°F (260°C) before it starts working at 50% effectiveness. When fully effective, the converter reaches a temperature range of 900° to 1,600°F (482° to 871°C).

CERAMIC MONOLITH CATALYTIC CONVERTER Converter Usage
A catalytic converter must be located as close as possible to the exhaust manifold to work effectively. The farther back the converter is positioned in the exhaust system, the more gases cool before they reach the converter.

OBD-II CATALYTIC CONVERTER PERFORMANCE
With OBD-II equipped vehicles, catalytic converter performance is monitored by heated oxygen sensor (HO2S), both before and after the converter. FIGURE The OBD-II catalytic converter monitor compares the signals of the upstream and downstream HO2S to determine converter efficiency.

CONVERTER-DAMAGING CONDITIONS
Since converters have no moving parts, they require no periodic service. Under federal law, catalyst effectiveness is warranted for 80,000 miles or 8 years. The three main causes of premature converter failure are: Contamination. Excessive temperatures. Improper air–fuel mixtures.

DIAGNOSING CATALYTIC CONVERTERS The Tap Test
The simple tap test involves tapping (not pounding) on the catalytic converter using a rubber mallet. If the substrate inside the converter is broken, the converter will rattle when hit. If the converter rattles, a replacement converter is required.

This can be accomplished in one of the following ways:
DIAGNOSING CATALYTIC CONVERTERS Testing Backpressure with a Pressure Gauge Exhaust system backpressure can be measured directly by installing a pressure gauge in an exhaust opening. This can be accomplished in one of the following ways: To test an oxygen sensor, remove the inside of an old, discarded oxygen sensor and thread in an adapter to convert it to a vacuum or pressure gauge.

DIAGNOSING CATALYTIC CONVERTERS Testing Backpressure with a Pressure Gauge
To test an exhaust gas recirculation (EGR) valve, remove the EGR valve and fabricate a plate. To test an air injection reaction (AIR) check valve, remove the check valve from the exhaust tubes leading to the exhaust manifold. Use a rubber cone with a tube inside to seal against the exhaust tube. Connect the tube to a pressure gauge.

DIAGNOSING CATALYTIC CONVERTERS Testing Backpressure with a Pressure Gauge
FIGURE A backpressure tool can be made by using an oxygen sensor housing and using epoxy or braze to hold the tube to the housing.

DIAGNOSING CATALYTIC CONVERTERS Testing a Catalytic Converter for Temperature Rise
To test the converter, operate the engine at 2500 RPM for at least 2 minutes to fully warm up the converter. Measure the inlet and the outlet temperatures using an infrared pyrometer

DIAGNOSING CATALYTIC CONVERTERS Testing a Catalytic Converter for Temperature Rise
FIGURE The temperature of the outlet should be at least 10% hotter than the temperature of the inlet. If a converter is not working, the inlet temperature will be hotter than the outlet temperature.

DIAGNOSING CATALYTIC CONVERTERS Catalytic Converter Efficiency Tests
The efficiency of a catalytic converter can be determined using an exhaust gas analyzer. Oxygen level test. Snap-throttle test.

OBD-II CATALYTIC CONVERTER MONITOR
The catalytic converter monitor of OBD II uses an upstream and downstream HO2S to test catalyst efficiency. When the engine combusts a lean air–fuel mixture, higher amounts of oxygen flow through the exhaust into the converter. The catalyst materials absorb this oxygen for the oxidation process, thereby removing it from the exhaust stream. If a converter cannot absorb enough oxygen, oxidation does not occur.

CATALYTIC CONVERTER REPLACEMENT GUIDELINES
Because a catalytic converter is a major exhaust gas emission control device, the Environmental Protection Agency (EPA) has strict guidelines for its replacement, including: If a converter is replaced on a vehicle with less than 80,000 miles/8 years, depending on the year of the vehicle, an original equipment catalytic converter must be used as a replacement.

The replacement converter must be of the same design as the original. If the original had an air pump fitting, so must the replacement. The old converter must be kept for possible inspection by the authorities for 60 days. A form must be completed and signed by both the vehicle owner and a representative from the service facility. This form must state the cause of the converter failure and must remain on file for 2 years.

EVAPORATIVE EMISSION CONTROL SYSTEM
The purpose of the evaporative (EVAP) emission control system is to trap and hold gasoline vapors also called volatile organic compounds, or VOCs. The charcoal canister is part of an entire system of hoses and valves called the evaporative control system.

EVAP Components How the Evaporative Control System Works Vapor Purging Computer-Controlled Purge

FIGURE A typical bayonet-type gas cap.

FIGURE A charcoal canister can be located under the hood or underneath the vehicle.

FIGURE The evaporative emission control system includes all of the lines, hoses, and valves, plus the charcoal canister.

FIGURE A typical evaporative emission control system. Note that when the computer turns on the canister purge solenoid valve, manifold vacuum draws any stored vapors from the canister into the engine. Manifold vacuum also is applied to the pressure control valve. When this valve opens, fumes from the fuel tank are drawn into the charcoal canister and eventually into the engine. When the solenoid valve is turned off (or the engine stops and there is no manifold vacuum), the pressure control valve is spring-loaded shut to keep vapors inside the fuel tank from escaping to the atmosphere.

NONENHANCED EVAPORATIVE CONTROL SYSTEMS
Prior to 1996, evaporative systems were referred to as evaporative (EVAP) control systems. This term refers to evaporative systems that had limited diagnostic capabilities. While they are often PCM controlled, their diagnostic capability is usually limited to their ability to detect if purge has occurred.

ENHANCED EVAPORATIVE CONTROL SYSTEM
Beginning in 1996 with OBD-II vehicles, manufacturers were required to install systems that are able to detect both purge flow and evaporative system leakage. The systems on models produced between 1996 and 2000 have to be able to detect a leak as small as .040 in. diameter. Beginning in the model year 2000, the enhanced systems started a phase-in of .020-in.-diameter leak detection.

ENHANCED EVAPORATIVE CONTROL SYSTEM
Canister Vent Solenoid Valve Canister Purge Solenoid (CPS) Valve

LEAK DETECTION PUMP SYSTEM
Many Chrysler vehicles use a leak detection pump (LDP) as part of the evaporative control system diagnosis equipment. FIGURE A leak detection pump (LDP) used on some Chrysler vehicles to pressurize (slightly) the fuel system to check for leaks.

ONBOARD REFUELING VAPOR RECOVERY
The primary feature of most ORVR systems is the restricted tank filler tube, which is about 1 inch (25 mm) in diameter. This reduced-size filler tube creates an aspiration effect, which tends to draw outside air into the filler tube. During refueling, the fuel tank is vented to the charcoal canister, which captures the gas fumes and with air flowing into the filler tube, no vapors can escape to the atmosphere.

STATE INSPECTION EVAP TESTS
In some states, a periodic inspection and test of the fuel system are mandated along with a dynamometer test. The emissions inspection includes tests on the vehicle before and during the dynamometer test. Before the running test, the fuel tank and cap, fuel lines, canister, and other fuel system components must be inspected and tested to ensure that they are not leaking gasoline vapors into the atmosphere.

DIAGNOSING THE EVAP SYSTEM
Before vehicle emissions testing began in many parts of the country, little service work was done on the evaporative emission system. Common engine-performance problems that can be caused by a fault in this system include: Poor fuel economy. Poor performance.

LOCATING LEAKS IN THE SYSTEM
Leaks in the evaporative emission control system will cause the malfunction check gas cap indication lamp to light on some vehicles. FIGURE Some vehicles will display a message if an evaporative control system leak is detected that could be the result of a loose gas cap.

FIGURE To test for a leak, this tester was set to the inch hole and turned on. The ball rose in the scale on the left and the red arrow was moved to that location. If when testing the system for leaks, the ball rises higher than the arrow, then the leak is larger than If the ball does not rise to the level of the arrow, the leak is smaller than inch.

FIGURE This unit is applying smoke to the fuel tank through an adapter and the leak was easily found to be the gas cap seal.

FIGURE An emission tester that uses nitrogen to pressurize the fuel system.

EVAPORATIVE SYSTEM MONITOR
The EVAP system monitor tests for purge volume and leaks. Most applications purge the charcoal canister by venting the vapors into the intake manifold during cruise. To do this, the PCM typically opens a solenoid-operated purge valve installed in the purge line leading to the intake manifold.

EVAPORATIVE SYSTEM MONITOR
FIGURE The fuel tank pressure sensor (black unit with three wires) looks like a MAP sensor and is usually located on top of the fuel pump module (white unit).

ALWAYS TIGHTEN THE CAP CORRECTLY
FIGURE This Toyota cap has a warning—the check engine light will come on if not tightened until one click.

TYPICAL EVAP MONITOR The PCM will run the EVAP monitor when the following enable criteria are met. Typical enable criteria include: Cold start BARO greater than 70 kPa (20.7 in. Hg or 10.2 PSI) IAT between 39° and 86°F at engine start-up ECT between 39° and 86°F at engine start-up ECT and IAT within 39°F of each other at engine start-up Fuel level within 15% to 85% TP sensor between 9% and 35%

TYPICAL EVAP MONITOR Running the EVAP Monitor
Weak Vacuum Test (P0440—large leak). Small Leak Test (P0442—small leak). Excess Vacuum Test (P0446). Purge Solenoid Leak Test (P1442).

KEEP THE FUEL TANK PROPERLY FILLED
FIGURE The fuel level must be above 15% and below 85% before the EVAP monitor will run on most vehicles.

SUMMARY Recirculating 6% to 10% inert exhaust gases back into the intake system reduces peak temperature inside the combustion chamber and reduces NOX exhaust emissions. EGR is usually not needed at idle, at wide-open throttle, or when the engine is cold. Many EGR systems use a feedback potentiometer to signal the PCM the position of the EGR valve pintle. OBD II requires that the flow rate be tested and then is achieved by opening the EGR valve and observing the reaction of the MAP sensor. Positive crankcase ventilation (PCV) systems use a valve or a fixed orifice to transfer and control the fumes from the crankcase back into the intake system. A PCV valve regulates the flow of fumes depending on engine vacuum and seals the crankcase vent in the event of a backfire.

SUMMARY As much as 30% of the air needed by the engine at idle speed flows through the PCV system. The SAI system forces air at low pressure into the exhaust to reduce CO and HC exhaust emissions. A catalytic converter is an aftertreatment device that reduces exhaust emissions outside of the engine. A catalyst is an element that starts a chemical reaction but is not consumed in the process. The catalyst material used in a catalytic converter includes rhodium, palladium, and platinum. The OBD-II system monitor compares the relative activity of a rear oxygen sensor to the pre-catalytic oxygen sensor to determine catalytic converter efficiency.

SUMMARY The purpose of the evaporative emission (EVAP) control system is to reduce the release of volatile organic compounds (VOCs) into the atmosphere. A carbon (charcoal) canister is used to trap and hold gasoline vapors until they can be purged and run into the engine to be burned. OBD-II regulation requires that the evaporative emission control system be checked for leakage and proper purge flow rates. External leaks can best be located by pressurizing the fuel system with low-pressure smoke.

REVIEW QUESTIONS How does the use of exhaust gas reduce NOX exhaust emission? How does the DPFE sensor work? What exhaust emissions do the PCV valve and SAI system control? How does a catalytic converter reduce NOX to nitrogen and oxygen? How does the computer monitor catalytic converter performance? What components are used in a typical evaporative emission control system? How does the computer control the purging of the vapor canister?

CHAPTER QUIZ Two technicians are discussing clogged EGR passages. Technician A says clogged EGR passages can cause excessive NOX exhaust emission. Technician B says that clogged EGR passages can cause the engine to ping (spark knock or detonation). Which technician is correct? Technician A only Technician B only Both Technicians A and B Neither Technician A nor B

CHAPTER QUIZ 2. An EGR valve that is partially stuck open would most likely cause what condition? Rough idle/stalling Excessive NOX exhaust emissions Ping (spark knock or detonation) Missing at highway speed

CHAPTER QUIZ 3. How much air flows through the PCV system when the engine is at idle speed? 1% to 3% 5% to 10% 10% to 20% Up to 30%

CHAPTER QUIZ 4. Technician A says that if a PCV valve rattles, then it is okay and does not need to be replaced. Technician B says that if a PCV valve does not rattle, it should be replaced. Which technician is correct? Technician A only Technician B only Both Technicians A and B Neither Technician A nor B

CHAPTER QUIZ 5. The switching valves on the AIR pump have failed several times. Technician A says that a defective exhaust check valve could be the cause. Technician B says that a restricted exhaust system could be the cause. Which technician is correct? Technician A only Technician B only Both Technicians A and B Neither Technician A nor B

CHAPTER QUIZ 6. Two technicians are discussing testing a catalytic converter. Technician A says that a vacuum gauge can be used and observed to see if the vacuum drops with the engine at idle for 30 seconds. Technician B says that a pressure gauge can be used to check for backpressure. Which technician is correct? Technician A only Technician B only Both Technicians A and B Neither Technician A nor B

CHAPTER QUIZ 7. At about what temperature does oxygen combine with the nitrogen in the air to form NOX? 500°F (260°C) 750°F (400°C) 1,500°F (815°C) 2,500°F (1,370°C)

CHAPTER QUIZ 8. A P0401 is being discussed. Technician A says that a stuck-closed EGR valve could be the cause. Technician B says that clogged EGR ports could be the cause. Which technician is correct? Technician A only Technician B only Both Technicians A and B Neither Technician A nor B

CHAPTER QUIZ 9. Which EVAP valve(s) is (are) normally closed?
Canister purge valve Canister vent valve Both canister purge and canister vent valve Neither canister purge nor canister vent valve

CHAPTER QUIZ 10. Before an evaporative emission monitor will run, the fuel level must be where? At least 75% full Over 25% Between 15% and 85% The level of the fuel in the tank is not needed to run the monitor test

OBJECTIVES After studying Chapter 37, the reader will be able to:

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