Question 1

What causes the nitrogen and oxygen in the air to combine and form NOx?&#10;A)Heat above 2,500 F (1,370 C)&#10;B)Any spark will cause this to occur&#10;C)Chemical reaction in the catalytic converter&#10;D)Sunlight

Accepted Answer

The high temperatures above 2,500 F (1,370 C), such as those found in combustion engines, cause nitrogen and oxygen in the air to combine and form NOx (nitrogen oxides). This is a thermal reaction that does not typically occur at lower temperatures.

Question 2

Exhaust gas recirculation (EGR) is generally not needed under any of the following conditions EXCEPT ________.&#10;A)Cold engine&#10;B)Idle speed&#10;C)Wide open throttle (WOT)&#10;D)Cruise speed

Accepted Answer

EGR is not typically needed when the engine is cold, at idle speed, or at wide open throttle because these conditions do not produce the optimal circumstances for the EGR system to reduce NOx emissions effectively. However, during cruise speed, the engine operates under moderate load conditions, making it an ideal scenario for the EGR system to function and reduce NOx emissions by recirculating a portion of the exhaust gases back into the combustion chamber.

Question 3

Technician A says that a low-restriction exhaust system could prevent a back pressure-typeVacuum-controlled EGR valve from opening correctly. Technician B says restricted exhaust can cause the EGR valve position sensor to fail. Which technician is correct?

A)Technician A only
B)Technician B only
C)Both technicians A and B
D)Neither technician A nor B

Both technicians A and B

Accepted Answer

Both technicians are correct. A low-restriction exhaust system could prevent a back pressure-type vacuum-controlled EGR valve from opening correctly, and restricted exhaust can cause the EGR valve position sensor to fail.

Question 4

EGR is used to control which exhaust emission? A)Unburned hydrocarbons (HC) B)Carbon monoxide (CO) C)Oxides of nitrogen (NOx) D)Carbon dioxide (CO₂₎

Accepted Answer

EGR (Exhaust Gas Recirculation) is primarily used to reduce the amount of oxides of nitrogen (NOx) emissions by recirculating a portion of an engine's exhaust gas back to the engine cylinders, thereby diluting the oxygen in the intake gases and reducing the peak temperature during combustion.

Question 5

A typical EGR pintle-position sensor is what type of sensor?&#10;A)Piezoelectric&#10;B)Wheatstone bridge&#10;C)Potentiometer&#10;D)Rheostat

Accepted Answer

The EGR (Exhaust Gas Recirculation) pintle-position sensor typically uses a potentiometer to measure the position of the pintle. This type of sensor varies its resistance based on the position of the pintle, providing a variable voltage signal that corresponds to the pintle's position.

Question 6

OBD-II regulations require that the EGR system be tested. Technician A says that the PCM can monitor the commanded position of the EGR valve to determine if it is functioning correctly. Technician B says that the PCM can open the EGR valve and monitor for a change in the MAP sensor or oxygen sensor reading to detect if the system is functioning correctly. Which technician is correct?

A)Technician A only
B)Technician B only
C)Both technicians A and B
D)Neither technician A nor B

Accepted Answer

Both technicians A and B are correct. The PCM (Powertrain Control Module) can indeed monitor the commanded position of the EGR (Exhaust Gas Recirculation) valve to check its functionality, as stated by Technician A. Additionally, as Technician B mentions, the PCM can also open the EGR valve and monitor changes in the MAP (Manifold Absolute Pressure) sensor or oxygen sensor readings to determine if the EGR system is working correctly. Both methods are valid diagnostic approaches for the EGR system under OBD-II regulations.

Question 7

Blocking off the EGR valve passages will have no effect on the OBD-II system.

Accepted Answer

Blocking off the EGR (Exhaust Gas Recirculation) valve passages can cause the OBD-II (On-Board Diagnostics II) system to set a fault code because the system monitors the flow and operation of the EGR system as part of its emissions control strategy.

Question 8

Manually opening an EGR valve with a vacuum pump or scan tool will cause the engine to idle roughly or stall.

Accepted Answer

Manually opening the EGR (Exhaust Gas Recirculation) valve introduces exhaust gases into the intake manifold, which can disrupt the air-fuel mixture balance, leading to rough idling or stalling, especially if the engine is at idle or low load conditions where it's not designed to handle large amounts of EGR flow.

Question 9

When testing an EGR system for proper operation using a vacuum gauge, how much should intake manifold vacuum drop when the EGR valve is commanded open by a scan tool?&#10;A)6-8 PSI&#10;B)6-8 in. Hg.&#10;C)1-2 in. Hg.&#10;D)14.7 PSI

Accepted Answer

When the EGR valve is commanded open, the intake manifold vacuum should drop by about 6-8 inches of mercury (in. Hg). This is because the EGR system recirculates a portion of an engine's exhaust gas back to the engine cylinders, reducing the oxygen content in the intake air, which in turn reduces peak combustion temperatures and reduces NOx emissions. The drop in vacuum is a result of the introduction of this exhaust gas into the intake manifold, which disrupts the vacuum being generated by the engine's intake stroke.

Question 10

A P0401 DTC (exhaust gas recirculation flow insufficient) is being discussed. Technician A says that a defective EGR valve could be the cause. Technician B says that clogged EGR passages could be the cause. Which technician is correct?

A)Technician A only
B)Technician B only
C)Both technicians A and B
D)Neither technician A nor B

Accepted Answer

Both a defective EGR valve and clogged EGR passages can lead to insufficient exhaust gas recirculation flow, which would trigger a P0401 diagnostic trouble code.

Question 11

The following statements are all correct EXCEPT ________.&#10;A)Many vehicles use the MAP sensor to monitor EGR operation&#10;B)The MIL will be turned on after the second failure&#10;C)OBD-II vehicles require monitoring of the EGR system&#10;D)Linear EGR systems require exhaust backpressure

Accepted Answer

The answer of The following statements are all correct EXCEPT...

Question 12

A vehicle with a linear EGR valve has a piece of carbon stuck in the valve, causing it to be partially open all the time. What symptom would this cause?&#10;A)Stalling&#10;B)High exhaust system pressure&#10;C)Both A and B&#10;D)Neither A nor B

Accepted Answer

The answer of A vehicle with a linear EGR valve...

Question 13

The linear EGR valve uses ________ to control the opening of the valve.&#10;A)Vacuum&#10;B)A pressure valve&#10;C)A pulse-width modulated solenoid&#10;D)None of these

Accepted Answer

The answer of The linear EGR valve uses ________ to...

Question 14

In which of the following conditions is EGR not commanded?&#10;A)Cold engine&#10;B)Wide open throttle&#10;C)Idle&#10;D)All of these are correct.

Accepted Answer

The answer of In which of the following conditions is...

Question 15

Which of the following are symptoms of a clogged EGR passage?&#10;A)Poor performance and lack of power.&#10;B)Detonation during acceleration or cruise&#10;C)Reduced NOx emissions&#10;D)Rough idle and stalling

Accepted Answer

The answer of Which of the following are symptoms of...

Deck 84: Exhaust Gas Recirculation Systems