Question 1

Technician A says a pressure gauge can be inserted into the oxygen sensor bore, and back pressure caused by the catalytic converter can be measured. Technician B says a vacuum gauge can be used to identify a restricted converter. Who is correct?

Accepted Answer

Both technicians are correct. Technician A is correct in stating that a pressure gauge can be inserted into the oxygen sensor bore to measure back pressure caused by a catalytic converter, which is a common diagnostic technique. Technician B is also correct because a vacuum gauge can be used to diagnose a variety of engine issues, including a restricted catalytic converter, by observing the vacuum levels at different engine speeds.

Question 2

Technician A says retrieving DTCs from the control system is the best beginning for diagnosing emission problems. Technician B says because a single emissions system component failure can set multiple DTCs, codes should be used only to confirm the effectiveness of the repairs. Who is correct?

Accepted Answer

The answer of Technician A says retrieving DTCs from the...

Question 3

Crankcase pressure forcing crankcase gases through the clean air hose and into the air cleaner is being discussed. Technician A says the cause may be an excessive amount of blowby. Technician B says the cause may be a restricted PCV valve. Who is correct?

Accepted Answer

Both Technician A and Technician B are correct. Excessive blowby can increase crankcase pressure, forcing gases through the clean air hose into the air cleaner. Similarly, a restricted PCV (Positive Crankcase Ventilation) valve can cause increased crankcase pressure for the same reason, as it fails to properly vent these gases.

Question 4

Which of the following is a cause of detonation?

Accepted Answer

All the options listed are causes of detonation because they all lead to a failure in the Exhaust Gas Recirculation (EGR) system, which is designed to reduce detonation by recirculating a portion of an engine's exhaust gas back to the engine cylinders, lowering the combustion temperature.

Question 5

Technician A says if the EGR valve does not open, the engine may emit excessive amounts of HC. Technician B says if the EGR valve does not open, the engine may detonate on acceleration. Who is correct?

Accepted Answer

Technician B is correct because if the EGR (Exhaust Gas Recirculation) valve does not open, it can lead to increased combustion temperatures, which in turn can cause engine detonation or "knocking" during acceleration. The EGR valve's purpose is to recirculate a portion of the exhaust gases back into the combustion chamber to cool the combustion temperature, thereby reducing NOx emissions and preventing detonation. Technician A's statement about excessive HC (hydrocarbons) emissions is incorrect in this context; HC emissions are more directly related to incomplete combustion or issues with the ignition system, not the operation of the EGR valve.

Question 6

Technician A says the AIRB valve directs secondary air either to the intake manifold or to the catalytic converter. Technician B says with the engine at normal operating temperature, the AIR system sometimes goes back into upstream mode with the engine idling. Who is correct?

Accepted Answer

The answer of Technician A says the AIRB valve directs...

Question 7

The customer complains of a loss of power at highway speeds and a rough running engine at all speeds. A five-gas analyzer reveals these measurements at 2,500 rpm: HC = 700 ppm, CO = 0.2%, CO₂ = 9.2%, O₂ = 6.2%, and NO _X = 330 ppm. What is the most likely cause?

Accepted Answer

The high HC (hydrocarbons) level indicates unburned fuel, which, along with the normal CO (carbon monoxide) level, suggests incomplete combustion rather than a rich or lean mixture. This scenario is indicative of a lean misfire, where the engine misfires due to a lean fuel mixture, leading to rough running and loss of power.

Question 8

Excessively high HC emissions may be caused by ______.

Accepted Answer

Excessively high hydrocarbon (HC) emissions can be caused by ignition system misfiring and improper ignition timing, both of which can lead to incomplete combustion of fuel in the engine.

Question 9

Excessively high CO emissions may be caused by a ______.

Accepted Answer

Excessively high CO (carbon monoxide) emissions are typically caused by a rich air/fuel mixture, which can result from higher than normal fuel pressure. A lean mixture or a missing air filter would not cause high CO emissions.

Question 10

Technician A says a defective throttle position (TP)sensor will not affect the EGR valve operation. Technician B says a defective engine coolant temperature (ECT)sensor will not affect the EGR valve operation. Who is correct?

Accepted Answer

A defective throttle position sensor can affect EGR valve operation because the EGR system may use throttle position information to regulate exhaust gas recirculation. Similarly, a defective engine coolant temperature sensor can affect EGR valve operation because the EGR system may also use coolant temperature information to determine when and how much to recirculate.

Question 11

Technician A says CO emissions increase as the air/fuel ratio becomes richer. Technician B says CO emissions increase as the air/fuel ratio becomes leaner. Who is correct?

Accepted Answer

CO emissions increase as the air/fuel mixture becomes richer because more carbon monoxide is produced when there is not enough oxygen to fully combust the fuel, leading to incomplete combustion.

Question 12

Technician A says when CO goes up, O₂ goes down. Technician B says at the stoichiometric point (14.7:1), HC and CO will be at their lowest levels and CO₂ will be at its highest. Who is correct?

Accepted Answer

Both technicians are correct. Technician A is correct because when CO (carbon monoxide) levels increase, it indicates a rich fuel mixture, which leads to a decrease in oxygen sensor voltage (O₂ refers to an oxygen sensor reading). Technician B is correct because at the stoichiometric air-fuel ratio of 14.7:1, combustion is most efficient, resulting in the lowest levels of HC (hydrocarbons) and CO, and the oxygen sensor voltage will be at its optimal level, indicating a balanced air-fuel mixture.

Question 13

A scan tool can be used to diagnose a faulty ______.

Accepted Answer

A scan tool can diagnose a wide range of vehicle issues, including those related to a knock sensor, EVR solenoid, and the EVAP system, making all the provided options correct.

Question 14

When the engine is running at peak efficiency, the only gas that is desirable to be at its peak level is ______.

Accepted Answer

CO2 is the desirable gas to be at its peak level when an engine is running efficiently, as it indicates complete combustion of fuel.

Question 15

A typical four-gas exhaust analyzer does not measure ____ emissions.

Accepted Answer

A typical four-gas exhaust analyzer measures CO, CO2, HC, and O2 emissions, but not NOx emissions.

Question 16

Technician A says a defective PCV valve may cause rough idle operation. Technician B says the PCV system depends upon a properly sealed engine to perform correctly. Who is correct?

Accepted Answer

Both technicians are correct. A defective PCV (Positive Crankcase Ventilation) valve can indeed cause rough idle operation by disrupting the engine's air-fuel mixture. Technician B is also correct because the PCV system relies on a properly sealed engine to maintain the correct pressure and function effectively.

Question 17

Technician A says an I/M 240 test is four minutes long. Technician B says the test cycle includes acceleration, deceleration, and cruising on an actual road test. Who is correct?

Accepted Answer

Technician A is correct because the I/M 240 test, which stands for Inspection/Maintenance, is indeed a 240-second (or four-minute) test designed to simulate real driving conditions on a dynamometer to measure vehicle emissions. Technician B is incorrect because the test cycle simulates these conditions but does not involve an actual road test; it's conducted on a dynamometer in a controlled environment.

Question 18

A vehicle is in the shop because it failed an emissions test due to excessive carbon monoxide (CO). The fault was a bad oxygen sensor that was easily replaced. Technician A says that the EGR system should be checked before the vehicle is retested. Technician B says the vehicle should be tested with a five-gas analyzer before it is retested. Who is correct?

Accepted Answer

Both technicians are correct. Checking the EGR (Exhaust Gas Recirculation) system can help ensure it is functioning properly and not contributing to the emissions problem. Using a five-gas analyzer can provide a comprehensive view of the vehicle's emissions, including CO, to ensure the issue has been resolved before retesting.

Question 19

While discussing catalytic converter diagnosis, Technician A says a delta temperature test should be conducted. Technician B says a good converter is evident by low amounts of CO₂ in the tailpipe exhaust. Who is correct?

Accepted Answer

Technician A is correct because a delta temperature test, which measures the temperature difference before and after the catalytic converter, is a common method for assessing its efficiency. Technician B's statement is incorrect because "CO₂" does not represent a known substance related to exhaust emissions or catalytic converter function.

Question 20

Technician A says cylinder misfiring causes a significant increase in HC emissions. Technician B says a dirty air filter may cause high CO emissions. Who is correct?

Accepted Answer

Both statements are correct. Cylinder misfiring leads to unburned fuel exiting the engine, significantly increasing hydrocarbon (HC) emissions. A dirty air filter restricts airflow to the engine, causing a rich fuel mixture and potentially higher carbon monoxide (CO) emissions.

Quiz 34: Emission Control Diagnosis and Service

Technician A says a pressure gauge can be inserted into the oxygen sensor bore, and back pressure caused by the catalytic converter can be measured. Technician B says a vacuum gauge can be used to identify a restricted converter. Who is correct?

Technician A says retrieving DTCs from the control system is the best beginning for diagnosing emission problems. Technician B says because a single emissions system component failure can set multiple DTCs, codes should be used only to confirm the effectiveness of the repairs. Who is correct?

Crankcase pressure forcing crankcase gases through the clean air hose and into the air cleaner is being discussed. Technician A says the cause may be an excessive amount of blowby. Technician B says the cause may be a restricted PCV valve. Who is correct?

Which of the following is a cause of detonation?

Technician A says if the EGR valve does not open, the engine may emit excessive amounts of HC. Technician B says if the EGR valve does not open, the engine may detonate on acceleration. Who is correct?

Technician A says the AIRB valve directs secondary air either to the intake manifold or to the catalytic converter. Technician B says with the engine at normal operating temperature, the AIR system sometimes goes back into upstream mode with the engine idling. Who is correct?

The customer complains of a loss of power at highway speeds and a rough running engine at all speeds. A five-gas analyzer reveals these measurements at 2,500 rpm: HC = 700 ppm, CO = 0.2%, CO₂ = 9.2%, O₂ = 6.2%, and NO _X = 330 ppm. What is the most likely cause?

Excessively high HC emissions may be caused by ______.

Excessively high CO emissions may be caused by a ______.

Technician A says a defective throttle position (TP) sensor will not affect the EGR valve operation. Technician B says a defective engine coolant temperature (ECT) sensor will not affect the EGR valve operation. Who is correct?

Technician A says CO emissions increase as the air/fuel ratio becomes richer. Technician B says CO emissions increase as the air/fuel ratio becomes leaner. Who is correct?

Technician A says when CO goes up, O₂ goes down. Technician B says at the stoichiometric point (14.7:1) , HC and CO will be at their lowest levels and CO₂ will be at its highest. Who is correct?

A scan tool can be used to diagnose a faulty ______.

When the engine is running at peak efficiency, the only gas that is desirable to be at its peak level is ______.

A typical four-gas exhaust analyzer does not measure ____ emissions.

Technician A says a defective PCV valve may cause rough idle operation. Technician B says the PCV system depends upon a properly sealed engine to perform correctly. Who is correct?

Technician A says an I/M 240 test is four minutes long. Technician B says the test cycle includes acceleration, deceleration, and cruising on an actual road test. Who is correct?

While discussing catalytic converter diagnosis, Technician A says a delta temperature test should be conducted. Technician B says a good converter is evident by low amounts of CO₂ in the tailpipe exhaust. Who is correct?

Technician A says cylinder misfiring causes a significant increase in HC emissions. Technician B says a dirty air filter may cause high CO emissions. Who is correct?

Quiz 34: Emission Control Diagnosis and Service

Technician A says a pressure gauge can be inserted into the oxygen sensor bore, and back pressure caused by the catalytic converter can be measured. Technician B says a vacuum gauge can be used to identify a restricted converter. Who is correct?

Technician A says retrieving DTCs from the control system is the best beginning for diagnosing emission problems. Technician B says because a single emissions system component failure can set multiple DTCs, codes should be used only to confirm the effectiveness of the repairs. Who is correct?

Crankcase pressure forcing crankcase gases through the clean air hose and into the air cleaner is being discussed. Technician A says the cause may be an excessive amount of blowby. Technician B says the cause may be a restricted PCV valve. Who is correct?

Which of the following is a cause of detonation?

Technician A says if the EGR valve does not open, the engine may emit excessive amounts of HC. Technician B says if the EGR valve does not open, the engine may detonate on acceleration. Who is correct?

Technician A says the AIRB valve directs secondary air either to the intake manifold or to the catalytic converter. Technician B says with the engine at normal operating temperature, the AIR system sometimes goes back into upstream mode with the engine idling. Who is correct?

The customer complains of a loss of power at highway speeds and a rough running engine at all speeds. A five-gas analyzer reveals these measurements at 2,500 rpm: HC = 700 ppm, CO = 0.2%, CO2 = 9.2%, O2 = 6.2%, and NO X = 330 ppm. What is the most likely cause?

Excessively high HC emissions may be caused by ______.

Excessively high CO emissions may be caused by a ______.

Technician A says a defective throttle position (TP) sensor will not affect the EGR valve operation. Technician B says a defective engine coolant temperature (ECT) sensor will not affect the EGR valve operation. Who is correct?

Technician A says CO emissions increase as the air/fuel ratio becomes richer. Technician B says CO emissions increase as the air/fuel ratio becomes leaner. Who is correct?

Technician A says when CO goes up, O2 goes down. Technician B says at the stoichiometric point (14.7:1) , HC and CO will be at their lowest levels and CO2 will be at its highest. Who is correct?

A scan tool can be used to diagnose a faulty ______.

When the engine is running at peak efficiency, the only gas that is desirable to be at its peak level is ______.

A typical four-gas exhaust analyzer does not measure ____ emissions.

Technician A says a defective PCV valve may cause rough idle operation. Technician B says the PCV system depends upon a properly sealed engine to perform correctly. Who is correct?

Technician A says an I/M 240 test is four minutes long. Technician B says the test cycle includes acceleration, deceleration, and cruising on an actual road test. Who is correct?

While discussing catalytic converter diagnosis, Technician A says a delta temperature test should be conducted. Technician B says a good converter is evident by low amounts of CO2 in the tailpipe exhaust. Who is correct?

Technician A says cylinder misfiring causes a significant increase in HC emissions. Technician B says a dirty air filter may cause high CO emissions. Who is correct?

The customer complains of a loss of power at highway speeds and a rough running engine at all speeds. A five-gas analyzer reveals these measurements at 2,500 rpm: HC = 700 ppm, CO = 0.2%, CO₂ = 9.2%, O₂ = 6.2%, and NO _X = 330 ppm. What is the most likely cause?

Technician A says when CO goes up, O₂ goes down. Technician B says at the stoichiometric point (14.7:1) , HC and CO will be at their lowest levels and CO₂ will be at its highest. Who is correct?

While discussing catalytic converter diagnosis, Technician A says a delta temperature test should be conducted. Technician B says a good converter is evident by low amounts of CO₂ in the tailpipe exhaust. Who is correct?