ASE - Automotive Service Excellence Practice Test (F1: Compressed Natural Gas (CNG) Vehicles) 1

Question 1

Which component in a CNG fuel system is responsible for reducing high-pressure fuel from the cylinder to a usable pressure for the engine?

Accepted Answer

Pressure regulator

Answer

Fuel injector rail

Answer

Manual shutoff valve

Answer

CNG filter/separator

Question 2

A technician detects a natural gas odor around a CNG vehicle in an enclosed shop. What is the FIRST action that should be taken?

Accepted Answer

Immediately ventilate the area and move the vehicle outdoors

Answer

Use a manometer to locate the leak source

Answer

Apply soapy water to all fittings to find the leak

Answer

Disconnect the high-pressure fuel line at the cylinder

Question 3

What type of valve on a CNG cylinder automatically stops fuel flow if the downstream fuel line is severed or ruptures?

Accepted Answer

Excess flow valve

Answer

Manual shutoff valve

Answer

Pressure relief device (PRD)

Answer

Fuel temperature sensor

Question 4

During inspection of a CNG vehicle, a technician finds a cylinder with visible deep gouges and abrasion damage on its surface. What is the correct procedure?

Accepted Answer

Remove the cylinder from service immediately

Answer

Clean the cylinder and re-inspect it after 1,000 miles

Answer

Fill the cylinder and perform a hydrostatic pressure test

Answer

Apply epoxy filler to the damaged area and re-label the cylinder

Question 5

What is the purpose of the Pressure Relief Device (PRD) installed on CNG fuel cylinders?

Accepted Answer

To vent cylinder pressure if the cylinder temperature rises dangerously, such as during a fire

Answer

To regulate fuel delivery pressure to the injectors

Answer

To prevent overfilling during the fueling process

Answer

To measure remaining fuel quantity and send a signal to the fuel gauge

Question 6

A CNG vehicle cranks normally but will not start. The technician confirms the cylinder has adequate fuel pressure, the ignition system is functioning, and there are no communication codes. Which CNG-specific component should be suspected next?

Accepted Answer

Fuel lock-off solenoid valve

Answer

Oxygen sensor

Answer

Catalytic converter

Answer

Mass airflow sensor