Deck 18: Exhaust Aftertreatment Systems

Question 1

Technician A says that lean NOx traps (LNTs) are used by only light-duty diesel engines. Technician B says that LNTs are used by light- and heavy-duty diesel engines. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Answer 1

A

Question 2

Technician A says diesel exhaust oxidation catalysts used by diesel engines are like those used in automobiles for the last two decades. Technician B says diesel exhaust oxidation catalysts will store noxious emissions in the substrate when the exhaust temperatures are low. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Answer 2

B

Question 3

Technician A says the problem with using automobile catalysts in the exhaust system of diesel engines is the system's excess air and cool temperatures. Technician B says diesel exhaust catalysts need to be designed to withstand the higher exhaust temperatures of a diesel engine and its exhaust's lower oxygen content. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Answer 3

A

Question 4

Which of the following strategies is typically used to actively regenerate a catalyzed DPF?

A)Retarding injection timing.
B)Injecting fuel into the exhaust.
C)Heating the oxidation converter with a flame.
D)Placing the engine under load and driving above 45 mph (72 kph) for 30 minutes.

Question 5

Which strategy will most likely be used to passively regenerate a catalyzed DPF?

A)A stationary vehicle with raised idle and a partially closed intake throttle.
B)Using OEM software or a scanner to perform regeneration (light-duty vehicles only).
C)Driving at speeds above 45 mph (72 kph) for a minimum of 20 minutes.
D)Logging a fault code for a DPF with 80% or more soot loading.

Question 6

Which of the following is the function of an intake throttle valve on a diesel engine equipped with a DPF?

A)To increase exhaust backpressure.
B)To increase exhaust temperature.
C)To decrease cylinder EGR content.
D)To increase engine retarding force when decelerating with compression release brakes.

Question 7

Dosing the exhaust system of a 2007 diesel engine with fuel is necessary to do which of the following?

A)Regenerate the oxidation converter.
B)Add urea or diesel exhaust fluid (DEF) for NOx reduction.
C)Actively regenerate a catalyzed DPF.
D)Actively regenerate the CO adsorber.

Question 8

Consider a 2018 school bus that has the DPF warning lamp illuminated. The amber light is on steadily. What is the most correct service recommendation?

A)Drive the vehicle under load at a moderate speed for 20-40 minutes.
B)Use a dash switch to initiate a stationary regeneration.
C)Use OEM software to initiate an active regeneration.
D)Tow the vehicle to a service location and replace the
DPF)

Question 9

The DPF warning light and the red shutdown warning lamp are flashing. Technician A says the DPF filter needs to be removed and replaced. Technician B says the DPF needs an active regeneration. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Question 10

Technician A says nitric oxide (NO) is used by the DPF to convert soot to harmless emissions. Technician B says that the SCR catalysts cause NO to be converted into harmless emissions. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Question 11

Technician A says that without the pressure differential sensor (delta P sensor), the exhaust DPF would not regenerate, because the amount of soot loading would not be able to be properly calculated. Technician B says that the amount of soot loading is only estimated, and not accurately measured, using the delta P sensor. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Question 12

Catalyzed DPFs require oil with which of the following qualities?

A)No biodiesel contamination.
B)High viscosity index (VI).
C)Low ash content.
D)High alkalinity.

Question 13

Which process is used to clean ash from a DPF?

A)Active regeneration.
B)Passive regeneration.
C)Filter replacement.
D)Removal and back-flushing with compressed air.

Question 14

Technician A recommends that customers have the DPF removed and cleaned once a year. Technician B says the DPF needs to be actively regenerated at every oil change. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Question 15

The use of SCR and DPFs requires which type of fuel?

A)Low-sulfur diesel (LSD) fuel with under 500 ppm sulfur.
B)Ultra-low-sulfur diesel (ULSD) fuel with under 15 ppm sulfur.
C)Biodiesel mixed with regular petroleum fuel.
D)Biodiesel only

Question 16

Using SCR delivers which of the following?

A)Improved fuel economy and fewer DPF regenerations because injection timing is advanced.
B)Improved fuel economy and fewer DPF regenerations because injection timing is retarded.
C)Improved fuel economy and fewer DPF regenerations because DEF increases combustion efficiency.
D)Only lower NOx emissions.

Question 17

A slip catalyst located after the SCR catalyst converts _________.

A)NOx to N2
B)NH3 to N2
C)soot to CO₂ and N₂
D)fuel to heat through flameless combustion

Question 18

The SCR reservoir of a 2010 pickup truck has been completely depleted for more than 10 hours of driving time and the engine power has derated. Technician A says the correct service recommendation is to fill the DEF reservoir and clear associated fault codes to return the vehicle to service and full power. Technician B says the correct procedure is to fill the DEF reservoir and prime the DEF lines to remove the derate condition. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Question 19

Technician A says that DEF is always evacuated from lines and valves after the vehicle has shut down to prevent DEF from crystalizing and plugging the SCR system. Technician B says that DEF is removed to prevent it from freezing and causing damage. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Question 20

After two technicians examine a broken and disintegrated DPF filter, Technician A says the filter damage was caused by water contamination. Technician B says the filter was damaged by back-to-back regenerations that occurred too frequently. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Question 21

Which of the following is an in-cylinder method used by manufacturers to prevent emission formation?

A)DPF (diesel particulate filter)"
B)SCR (selective catalyst reduction)"
C)Oxidation catalyst
D)EGR (exhaust gas recirculation)"

Question 22

How many distinct stages of exhaust aftertreatment systems are used based on the progressively more restrictive Environmental Protection Agency (EPA) emission standards?

A)1"
B)2"
C)3
D)4"

Question 23

The alternative to SCR (selective catalyst reduction)-liquid (SCR-L) systems using DEF was to manufacture:

A)ammonia onboard in exhaust catalysts"
B)DPF (diesel particulate filter)"
C)advanced EGR systems using a throttle valve
D)oxidation catalysts"

Question 24

Diesel particulate filters, which trap soot emissions, became mandatory in:

A)2008"
B)2007"
C)2002
D)2005"

Question 25

Which of the following is NOT a common exhaust catalyst element in the exhaust aftertreatment systems being used on contemporary diesel engines?

A)SCR using hydrogen reduction (SCR-H)"
B)DPF combined with an SCR"
C)DPF with SCR-coating (SDPF)
D)Nitrogen slip catalysts"

Question 26

Technician A says the problem with using automobile catalysts in the exhaust system of diesel engines is the system's excess air and cool temperatures. Technician B says diesel exhaust catalysts need to be designed to withstand the higher exhaust temperatures of a diesel engine and its exhaust's lower oxygen content. Who is correct?

A)Technician A"
B)Technician B"
C)Both A and B
D)Neither A nor B"

Question 27

When comparing types of catalytic technology used by diesel engines and spark-ignition engines, which of the following catalyst technologies reduces just NOx (oxides of nitrogen)?

A)Two-way (oxidation) catalytic converter"
B)Three-way catalytic converter"
C)DOC (diesel oxidation catalyst)
D)Selective catalytic reduction using liquid (SCR-L)"

Question 28

A conventional oxidation catalytic converter found on a gasoline-fueled vehicle requires exhaust temperatures as high as ____ for catalysts to operate effectively.

A)932°F"
B)832°F"
C)600°F
D)500°F"

Question 29

What are chemical reactions called where oxygen is removed from NOx?

A)Induction"
B)Calcification"
C)Reduction
D)Oxidation"

Question 30

Which of the following causes oxygen to chemically combine with HC (hydrocarbons) and CO (carbon monoxide) at lower temperatures with the result of HC and CO being converted to carbon dioxide and water?

A)Oxidation catalytic converter"
B)Reduction catalytic converter"
C)DPF (diesel particulate filter)
D)Selective catalytic reduction using liquid (SCR-L)"

Question 31

Which strategy will most likely be used to passively regenerate a catalyzed DPF?

A)A stationary vehicle with raised idle and a partially closed intake throttle."
B)Using OEM software or a scanner to perform regeneration (light-duty vehicles only)."
C)Driving at speeds above 45 mph (72 kph) for a minimum of 20 minutes.
D)Logging a fault code for a DPF with 80% or more soot loading."

Question 32

Dosing the exhaust system of a 2007 diesel engine with fuel is necessary to do which of the following?

A)Regenerate the oxidation converter."
B)Add urea or diesel exhaust fluid (DEF) for NOx reduction."
C)Actively regenerate a catalyzed DPF.
D)Actively regenerate the CO adsorber."

Question 33

Technician A says that without the pressure differential sensor (delta P sensor), the exhaust DPF would not regenerate, because the amount of soot loading would not be able to be properly calculated. Technician B says that the amount of soot loading is only estimated, and not accurately measured, using the delta P sensor. Who is correct?

A)Technician A"
B)Technician B"
C)Both A and B
D)Neither A nor B"

Question 34

A fully loaded DPF (diesel particulate filter) may contain ____ of soot per liter of volume capacity.

A)2-3 grams"
B)1-2 grams"
C)10-12 grams
D)4-6 grams"

Question 35

Trapped soot and other trapped particles collected on the walls of the DPF (diesel particulate filter) will eventually plug the filter and produce:

A)low exhaust backpressure"
B)high exhaust backpressure"
C)high intake manifold pressure
D)high boost pressure"

Question 36

Which process is used to clean ash from a DPF?

A)Active regeneration."
B)Passive regeneration."
C)Filter replacement.
D)Removal and back-flushing with compressed air."

Question 37

Which of the following particles that cannot be regenerated does NOT end up in the DPF (diesel particulate filter)?

A)Soot trapped on filter walls"
B)Metals worn from internal engine parts"
C)Dirt particles bypassing the air intake, such as silica sand
D)Inorganic additives"

Question 38

OEM rebuilders have observed a relationship between increased ash loading in DPF (diesel particulate filter) and the likelihood for a DPF to:

A)crack"
B)plug"
C)open up
D)explode"

Question 39

To extend DPF (diesel particulate filter) life caused by compacted ash and cracking, some fleets make it part of routine maintenance to remove and clean DPFs on a regular basis, more frequently than what is required by the:

A)ATA (American Trucking Association)"
B)Local or state government"
C)EPA (Environmental Protection Agency)
D)OEM recommendation"

Question 40

Which of the following will MOST LIKELY restrict gas flow through the DPF (diesel particulate filter)?

A)Hardened ash"
B)Hardened tar"
C)Soft ash
D)Embedded diesel fuel"

Question 41

The fleet average benchmark for NOx in 2010 was no more than:

A)0.009 grams/mile"
B)0.010 grams/mile"
C)0.007 grams/mile
D)0.017 grams/mile"

Question 42

What is the ammonia (NH3) compound DEF (diesel exhaust fluid) called that is essential to SCR (selective catalyst reduction) system operation?

A)Ammonia nitrate"
B)Nitrogen sulfate"
C)Uric
D)Urea"

Question 43

What NOX aftertreatment does not require onboard storage of liquid DEF, instead, produces ammonia inside a unique catalyst substrate through a multistep chemical process that uses hydrogen from fuel molecules and nitrogen from stored NOx?

A)SCR-L"
B)SCR-H"
C)SCR-U
D)NAC (nitrogen adsorbing catalysts)"

Question 44

What operation takes place during normal engine operating conditions, when no regeneration is taking place in the NAC (nitrogen adsorbing catalysts)?

A)Rich phase"
B)Stoichiometric phase"
C)Lean phase
D)Control phase"

Question 45

The hydrogen and carbon molecules in gasoline need oxygen to completely burn in a stoichiometric ratio of:

A)15.7:1"
B)17.7:1"
C)14.7:1
D)18.7:1"

Question 46

The SCR reservoir of a 2010 pickup truck has been completely depleted for more than 10 hours of driving time and the engine power has derated. Technician A says the correct service recommendation is to fill the DEF reservoir and clear associated fault codes to return the vehicle to service and full power. Technician B says the correct procedure is to fill the DEF reservoir and prime the DEF lines to remove the derate condition. Who is correct?

A)Technician A"
B)Technician B"
C)Both A and B
D)Neither A nor B"

Question 47

After two technicians examine a broken and disintegrated DPF filter, Technician A says the filter damage was caused by water contamination. Technician B says the filter was damaged by back-to-back regenerations that occurred too frequently. Who is correct?

A)Technician A"
B)Technician B"
C)Both A and B
D)Neither A nor B"

Question 48

Which is the more popular method commonly used to remove NOx from diesel exhaust gases?

A)Selective catalyst reduction with urea (SCR-U)"
B)NAC (nitrogen adsorbing catalysts)"
C)Selective catalyst reduction with Hydrogen (SCR-H)
D)LNT (lean NOxtTrap)"

Question 49

The liquid that contains the urea is called DEF and is rich in:

A)ammonia"
B)nitrogen"
C)hydrogen
D)nitrates"

Question 50

Two technicians are explaining SCR (selective catalyst reduction) operation. Technician A says that after the urea decomposes into ammonia in the mixing chamber, the ammonia-exhaust gas composition passes over an SCR catalyst containing either copper or iron to break apart NOx molecules. Technician B says that blades or screens in the mixing device are used to create exhaust gas turbulence ahead of the mixing chamber. Who is right?

A)A only"
B)B only"
C)Both A and B
D)Neither A nor B"

Question 51

To prevent adding diesel fuel to DEF (diesel exhaust fluid), the filler tube has a designated:

A)green color"
B)yellow color"
C)blue color
D)gray color"

Question 52

Which of the following DEF (diesel exhaust fluid) system component is NOT incorporated into a single module?

A)DEF controller (ECM)"
B)DEF-quality and DEF-level sensor"
C)DEF pump and reverting valve
D)DEF dosing valve"

Question 53

Two technicians are describing DEF (diesel exhaust fluid) operation. Technician A says that the amount of DEF used is in proportion to the amount of exhaust NOx. Technician B says that some DEF systems base the dosage on a probability of NOx in the exhaust system by using algorithms stored in the ECM. Who is right?

A)A only"
B)B only"
C)Both A and B
D)Neither A nor B"

Question 54

Which of the following procedures is used to control DEF (diesel exhaust fluid) dosing, formed between the NOx sensors, ammonia (NH3) sensors, an ECM, and the dosing valve in the latest systems?

A)Closed-loop feedback"
B)Open-loop feedback"
C)Exhaust backpressure
D)Boost pressure feedback"

Question 55

Which of these DEF (diesel exhaust fluid) states of operation comes after the engine starts and circulates DEF throughout the system, but in which no dosing takes place?

A)Heating state"
B)Priming state"
C)Dosing state
D)Purging state"

Question 56

A DEF warning and power derate takes place if the DEF (diesel exhaust fluid) level is:

A)filled"
B)changed"
C)leaking
D)depleted"

Question 57

Technician A says that once the DEF (diesel exhaust fluid) level becomes critical, vehicle speed will be limited. Technician B says that low DEF level display may be accompanied by a chime or voice message. Who is right?

A)A only"
B)B only"
C)Both A and B
D)Neither A nor B"

Question 58

Technician A says that the DEF (diesel exhaust fluid) reservoir will need to be filled with a minimum amount of fluid to operate above idle until the diesel exhaust fluid tank has been refilled. Technician A says that once the DEF level becomes critical, the engine will shut down. Who is right?

A)A only"
B)B only"
C)Both A and B
D)Neither A nor B"

Question 59

Two technicians are describing how to do a stationary regeneration. Technician A says that some SCR (selective reduction catalyst) systems can completely deplete the DEF (diesel exhaust fluid) before a fault code is set. Technician B says that after operating for more than 20 hours with depleted DEF, the vehicle will derate power. Who is right?

A)A only"
B)B only"
C)Both A and B
D)Neither A nor B"

Question 60

Which of the following tests is used to visually verify that the SCR (selective reduction catalyst) dosing injector is flowing in the correct quantity of DEF (diesel exhaust fluid)?

A)SCR visual leak check"
B)SCR system emptying"
C)SCR parameter reset
D)SCR dosing measurement test"