Question 1

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

Accepted Answer

The answer of The fleet average benchmark for NOx in...

Question 2

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

Accepted Answer

Urea is the compound used in diesel exhaust fluid (DEF) for selective catalyst reduction (SCR) systems to reduce nitrogen oxide emissions in diesel engines.

Question 3

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?

Accepted Answer

The answer of What NOX aftertreatment does not require onboard...

Question 4

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

Accepted Answer

During normal engine operating conditions, when no regeneration is taking place in the NAC, the engine typically operates in the lean phase, where the air-fuel mixture has more air than the stoichiometric ratio, allowing for efficient nitrogen oxide adsorption.

Question 5

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

Accepted Answer

The stoichiometric air-fuel ratio for gasoline is typically 14.7:1, meaning 14.7 parts of air to 1 part of fuel by mass for complete combustion.

Question 6

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?

Accepted Answer

The answer of The SCR reservoir of a 2010 pickup...

Question 7

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?

Accepted Answer

The answer of After two technicians examine a broken and...

Question 8

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

Accepted Answer

Selective catalyst reduction with urea (SCR-U) is the most popular method for removing NOx from diesel exhaust gases due to its high efficiency and effectiveness in reducing emissions.

Question 9

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

Accepted Answer

DEF (Diesel Exhaust Fluid) is a liquid used in diesel engines to reduce nitrogen oxide (NOx) emissions. It is composed of urea and water, and the urea is the component that is rich in nitrogen.

Question 10

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?

Accepted Answer

Technician A is correct about the role of the SCR catalyst in breaking apart NOx molecules using ammonia. Technician B is also correct that blades or screens are used to create turbulence for better mixing of exhaust gases and ammonia.

Question 11

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

Accepted Answer

The filler tube for DEF is typically blue to distinguish it from other fluids and prevent confusion with diesel fuel.

Question 12

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

Accepted Answer

The answer of Which of the following DEF (diesel exhaust...

Question 13

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?

Accepted Answer

Technician A is correct because DEF usage is proportional to the amount of NOx in the exhaust. Technician B is also correct because some systems use algorithms to estimate NOx levels and adjust DEF dosing accordingly.

Question 14

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?

Accepted Answer

Closed-loop feedback is used to control DEF dosing by continuously monitoring NOx and NH3 levels and adjusting the dosing accordingly to ensure optimal reduction of emissions.

Question 15

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?

Accepted Answer

The priming state occurs after the engine starts and circulates DEF throughout the system to prepare it for dosing, but no actual dosing takes place during this state.

Question 16

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

Accepted Answer

A DEF warning and power derate occur when the DEF level is depleted, as the system requires sufficient DEF to reduce emissions.

Question 17

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?

Accepted Answer

Both Technician A and Technician B are correct. When the DEF level becomes critically low, many vehicles will limit speed to encourage refilling. Additionally, a low DEF level is often indicated by a warning light, chime, or voice message to alert the driver.

Question 18

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?

Accepted Answer

The answer of Technician A says that the DEF (diesel...

Question 19

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?

Accepted Answer

The answer of Two technicians are describing how to do...

Question 20

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)?

Accepted Answer

The SCR dosing measurement test is specifically designed to verify the flow rate of DEF through the dosing injector, ensuring it is within the correct parameters.

Quiz 18: Exhaust Aftertreatment Systems