hw 10

Question 1

Surging at low speeds or a rough idle may occur if the EGR valve is stuck closed.

Answer 1

False

Question 2

Enable criteria are the conditions that have to be met in order for the PCM to run a specific test of a system.

Answer 2

True

Question 3

The OBD II AIR system is meant only to operate long enough to warm the exhaust and help promote catalytic converter light-off by burning left-over HC and CO in the exhaust manifold of a cold engine.

Answer 3

True

Question 4

Cylinders having excessive blow by may cause oil to be present in the air cleaner.

Answer 4

True’

Question 5

High oxygen levels are a good indicator of a rich air-fuel ratio.

Answer 5

False

Question 6

Misfiring of the ignition system may result in high hydrocarbon readings.

Answer 6

‘True’.

Question 7

If gasoline is allowed to evaporate into the air it becomes a significant source of hydrocarbon emissions.

Answer 7

True’.

Question 8

In a 2001 or newer OBD II system the PCM will set a code if the evaporative system has a leak as small as .020” in size.

Answer 8

True’.

Question 9

Technician A says oil accumulation in the air cleaner may indicate the PCV valve or hose is restricted. Technician B says a restricted PCV valve or hose may result in the accumulation of moisture and sludge in the engine and engine oil. Who is correct?

Answer 9

Both A and B

Question 10

In the PCV system, crankcase vapors are recycled to the:

Answer 10

Intake manifold

Question 11

Which exhaust gas /gasses are controlled by the EGR valve?

Answer 11

NOx

Question 12

The catalytic converter may be tested with the

a.

Delta temperature test
b.

O2 storage test
c.

Delta pressure feedback test
d.

Both A and B

Answer 12

Both A and B

Question 13

Excessive CO emissions may be caused by:

Answer 13

Rich air-fuel mixtures

Question 14

The OBD II AIR system pumps air into the;

Answer 14

Exhaust manifold

Question 15

The vent valve in an evaporative emissions system may be:
a.

Opened to allow fresh air through the charcoal canister
b.

Closed with the purge valve open while the PCM monitors the fuel tank pressure sensor for vacuum
c.

Closed to prevent the system from purging
d.

Both A and B

Answer 15

Both A and B

Question 16

Oxides of nitrogen (NOx) are formed when combustion temperatures reach more than:

Answer 16

2,500 degrees

Question 17

Excessive HC emissions may be caused by:

Answer 17

Ignition system defects
Vacuum leaks
Excessively lean or rich air-fuel ratio
All of the above

Question 18

Which exhaust gas is near its highest level when the air/fuel ratio is near stoichiometric?

Answer 18

CO2

Question 19

A three-way catalyst is named for its ability to reduce which emissions:

Answer 19

NOx, CO, and HC

Question 20

Fresh air is allowed to enter the charcoal canister:

Answer 20

When the PCM purges the canister

Question 21

Technician A says each module in a CAN system receives every communication on the serial data bus. Technician B says only the messages with the correct heading are responded to by a module in a CAN system. Who is correct?

Answer 21

Both A and B

Question 22

Bi-directional control means the:

Answer 22

Technician can tell a computer to exercise an output

Question 23

Technician A says an open in star network bus will affect all the modules on the network. Technician B says an open in a loop network will isolate a module from the network. Who is correct?

Answer 23

Neither A nor B

Question 24

The components of the PCM responsible for controlling circuits or devices are called:

Answer 24

Drivers

Question 25

All of the following are PCM actuators except:

Answer 25

PCV valve

Question 26

All of the following are the same communication protocol except:

Answer 26

ISO 9141

Question 27

What is the term used to define the operating conditions that must be present during a second trip to set a code?

Answer 27

Similar conditions

Question 28

A flashing MIL indicates a

Answer 28

Misfire that may damage the catalytic converter

Question 29

Technician A says PCMs in an OBD II system may have replaceable PROMs. Technician B says a new PCM will need to be flashed before it can be used in a vehicle. Who is correct?

Answer 29

Technician B only

Question 30

Technician A says long term fuel trim works to bring short term fuel trim close to zero percent correction. Technician B says if a lean condition exists because of a vacuum leak, the long term fuel trim will have a plus (+) number on the scan tool. Who is correct?

Answer 30

Both A and B

Question 31

The output voltage of a downstream O2 sensor is fluctuating when the engine is at operating temperature. Technician A says the catalytic converter is working efficiently. Technician B says the O2 sensor may need to be replaced. Who is correct?

Answer 31

Neither A nor B

Question 32

The MIL light of an OBD-equipped vehicle is flashing. Technician A says a spark plug wire may be shorted to ground. Technician B says a cylinder may have low compression. Who is correct?

Answer 32

Both A and B

Question 33

Technician A says enabling criteria defines the criteria that must be met before the vehicle will enter closed loop. Technician B says enabling criteria defines the criteria that must be met in order for a monitor test to be completed. Who is correct?

Answer 33

Both A and B

Question 34

The signal that alerts the misfire monitor that a misfire may be occurring is provided by the:

Answer 34

Crankshaft position sensor

Question 35

The PCM has the option of turning the MIL off when the diagnostic test which caused the MIL to light passes for:

Answer 35

Three consecutive trips

Question 36

Technician A says a type “A” misfire will set a trouble code on the first failure. Technician B says a type “B” misfire will set a trouble code on the first failure. Who is correct?

Answer 36

Technician A only

Question 37

Which of the following OBD-II test modes allows scan tools to access freeze frame data?

Answer 37

Mode 2

Question 38

Technician A says the basic advantage of the snapshot feature on a scan tool is the ability to look at the existing conditions (a single frame of data) when a code was set. Technician B says GM failure records do the same thing as a snapshot but also include any fault stored in memory, not just those related to the emissions-related circuits. Who is correct?

Answer 38

Neither A nor B

Question 39

The AIR pump is normally used:

Answer 39

On startup

Question 40

Technician A says an OBD II trip is the same as a drive cycle. Technician B says a trip is a period of operation that allows a monitor to complete. Who is correct?

Answer 40

Technician B only