• 57 questions

ASE F1 Study Guide

Unofficial study guide for ASE's F1 Compressed Natural Gas Vehicle test: its six content areas, with practice questions on each.

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Fuel economy is checked in gasoline gallon equivalents (GGE). About how much CNG is one GGE?

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Unofficial practice questions, not affiliated with the National Institute for Automotive Service Excellence (ASE). Bank checked October 14, 2026.

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All 57 questions with answers

Pre-service vehicle inspection 5

  • A CNG tank has passed its expiration date and shows no damage at all. What must be done with it? Answer: Replace it: a tank cannot be requalified. Source: US Department of Energy, Alternative Fuels Data Center, CNG Fuel System and Tank Maintenance, CNG Tank End-of-Life. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), A. Pre-Service Vehicle Inspection (5 of 55)
  • A CNG vehicle is checked against the applicable safety standards. To which vehicles does FMVSS No. 303, on CNG fuel system integrity, apply? Answer: Those of 10,000 pounds GVWR or less, and school buses of any weight. Source: 49 CFR 571.303 (FMVSS No. 303, Fuel system integrity of compressed natural gas vehicles), S3. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), A. Pre-Service Vehicle Inspection (5 of 55)
  • A pickup was converted to CNG after it was built. Where should the supplemental emission control information label of the conversion be? Answer: Next to the original emission control information label, if possible. Source: 40 CFR 85.530, paragraph (b). Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), A. Pre-Service Vehicle Inspection (5 of 55)
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Pre-service vehicle inspection, continued

  • The tank label cannot be read with the shields in place. Where else may the expiration date be found? Answer: On a label near the fueling connector or under the hood. Source: US Department of Energy, Alternative Fuels Data Center, CNG Fuel System and Tank Maintenance, CNG Tank End-of-Life. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), A. Pre-Service Vehicle Inspection (5 of 55)
  • Which two facts about the conversion itself must the supplemental emission label of a converted vehicle give? Answer: The date of conversion and the mileage at that time. Source: 40 CFR 85.530, paragraph (a)(5). Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), A. Pre-Service Vehicle Inspection (5 of 55)

CNG system equipment inspection 9

  • A pickup under 10,000 pounds GVWR has a CNG container. How often must the container be visually inspected, by the statement FMVSS No. 304 puts on its label? Answer: At least every 36 months or 36,000 miles, whichever comes first. Source: 49 CFR 571.304 (FMVSS No. 304, Compressed natural gas fuel container integrity), S7.4(g). Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), B. CNG System Equipment Inspection (8 of 55)
  • A required label on a CNG container has become unreadable. How long does FMVSS No. 304 require that label to stay in place and legible? Answer: For the maker's recommended service life of the container. Source: 49 CFR 571.304 (FMVSS No. 304, Compressed natural gas fuel container integrity), S7.4. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), B. CNG System Equipment Inspection (8 of 55)
  • In which units must a CNG container label state the service pressure, under FMVSS No. 304? Answer: In kPa and in psig. Source: 49 CFR 571.304 (FMVSS No. 304, Compressed natural gas fuel container integrity), S7.4(c). Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), B. CNG System Equipment Inspection (8 of 55)
  • What does the "Manufactured in" statement on a CNG container label give, under FMVSS No. 304? Answer: The month and year of manufacture of the container. Source: 49 CFR 571.304 (FMVSS No. 304, Compressed natural gas fuel container integrity), S7.4(b). Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), B. CNG System Equipment Inspection (8 of 55)
  • What may the fuel line from the tank to the fuel injection system of a CNG vehicle be made of, by the Alternative Fuels Data Center? Answer: A metal tube, a flexible hose, or a combination of the two. Source: US Department of Energy, Alternative Fuels Data Center, How Do Natural Gas Vehicles Work?, Key Components of a Natural Gas Vehicle. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), B. CNG System Equipment Inspection (8 of 55)
  • Where is the diamond label that identifies a vehicle as CNG fueled? Answer: On the lower right-hand side of the rear of the vehicle. Source: US Department of Energy, Alternative Fuels Data Center, Natural Gas Safety after a Traffic Accident, Inform First Responders. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), B. CNG System Equipment Inspection (8 of 55)
  • Which statement about the fuel must the label of every CNG fuel container carry, under FMVSS No. 304? Answer: CNG Only. Source: 49 CFR 571.304 (FMVSS No. 304, Compressed natural gas fuel container integrity), S7.4(f). Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), B. CNG System Equipment Inspection (8 of 55)
  • Which statement does FMVSS No. 303 require on the permanent label near the refueling connection, beside the service pressure? Answer: See instructions on fuel container for inspection and service life. Source: 49 CFR 571.303 (FMVSS No. 303, Fuel system integrity of compressed natural gas vehicles), S5.3. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), B. CNG System Equipment Inspection (8 of 55)
  • Why are CNG tanks mounted under the body of a vehicle at higher risk than tanks mounted elsewhere? Answer: Road debris and impacts, such as driving over a curb. Source: US Department of Energy, Alternative Fuels Data Center, CNG Fuel System and Tank Maintenance, CNG Storage Tank Inspection. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), B. CNG System Equipment Inspection (8 of 55)

Leak testing and repairs 7

  • A CNG car was in a collision that may have damaged the fuel system. Technician A says the manual shut-off valve for the storage tank should be closed, if it has one. Technician B says the car should be towed, and not driven if there is a danger of a leak. Who is right? Answer: Both technicians. Source: US Department of Energy, Alternative Fuels Data Center, Natural Gas Safety after a Traffic Accident, Get a Tow. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), C. Leak Testing and Repairs (6 of 55)
  • A repaired system is pressurized with CNG. Why does a slow time-fill usually give a fuller fill than a fast fill? Answer: The gas heats up less, so it stays denser. Source: US Department of Energy, Alternative Fuels Data Center, Filling CNG Fuel Tanks, Fueling rate. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), C. Leak Testing and Repairs (6 of 55)
  • A rotten egg odor comes from a closed garage where a CNG vehicle is parked. Why is a leak there more dangerous than one outdoors? Answer: The gas has limited area in which to disperse. Source: US Department of Energy, Alternative Fuels Data Center, Natural Gas Fuel Safety, Compressed Natural Gas. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), C. Leak Testing and Repairs (6 of 55)
  • A slight gas odor is noticed as the fueling nozzle is connected, and again as it is disconnected. What does that show? Answer: Nothing wrong: it is normal and should quickly dissipate. Source: US Department of Energy, Alternative Fuels Data Center, Natural Gas Fuel Safety, Compressed Natural Gas. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), C. Leak Testing and Repairs (6 of 55)
  • After a collision, a hissing noise comes from the rear of a CNG car. What does the Alternative Fuels Data Center tell the driver to do first, if it can be done? Answer: Close the manual shut-off valve. Source: US Department of Energy, Alternative Fuels Data Center, Natural Gas Safety after a Traffic Accident, CNG. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), C. Leak Testing and Repairs (6 of 55)
  • After a repair, a system rated at 3,600 psi is refilled with CNG on a 90 °F day. By the rule of thumb of the Alternative Fuels Data Center, about what pressure is a full fill? Answer: About 3,800 psi. Source: US Department of Energy, Alternative Fuels Data Center, Filling CNG Fuel Tanks, Pressure rating. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), C. Leak Testing and Repairs (6 of 55)
  • To allow for hot days and the heat of compression, up to what pressure can a tank rated at 3,600 psi technically be filled, by the Alternative Fuels Data Center? Answer: 4,500 psi. Source: US Department of Energy, Alternative Fuels Data Center, Filling CNG Fuel Tanks, Pressure rating. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), C. Leak Testing and Repairs (6 of 55)

Emissions and performance verification 11

  • A conversion is checked against EPA rules. When does 40 CFR 85.505 call a converted vehicle "new and relatively new"? Answer: When it is converted no later than the calendar year after its original model year. Source: 40 CFR 85.505, paragraph (b)(1). Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), D. Emissions and Performance Verification (11 of 55)
  • A conversion system is certified under 40 CFR 85.510. What must the OBD system of the converted vehicle do? Answer: Detect faults in monitored emission systems, with any new monitoring the fuel needs. Source: 40 CFR 85.510, paragraph (b)(9)(i). Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), D. Emissions and Performance Verification (11 of 55)
  • A driver says the fuel gauge shows a short fill after fueling on a hot afternoon, though the station reached its rated pressure. What explains it? Answer: Warm gas expands, so the tank takes less of its design potential. Source: US Department of Energy, Alternative Fuels Data Center, Filling CNG Fuel Tanks, introduction. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), D. Emissions and Performance Verification (11 of 55)
  • A gasoline truck converted to CNG is emission tested. To keep its exemption from the tampering prohibition, which requirements must the converted vehicle meet? Answer: Those that applied to the original vehicle. Source: 40 CFR 85.525, introductory text. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), D. Emissions and Performance Verification (11 of 55)
  • A natural gas vehicle is road tested for driveability. How should its horsepower and acceleration compare with those of an equivalent conventionally fueled vehicle? Answer: They are comparable. Source: US Department of Energy, Alternative Fuels Data Center, Natural Gas Vehicles, introduction. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), D. Emissions and Performance Verification (11 of 55)
  • A spark-ignited natural gas engine uses a three-way catalytic converter. What kind of combustion does a three-way converter need in order to reduce NOx? Answer: Stoichiometric or fuel-rich. Source: Wikipedia, Catalytic converter, lead section. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), D. Emissions and Performance Verification (11 of 55)
  • An emission test is run on a CNG vehicle. Which regulated tailpipe emissions does the Alternative Fuels Data Center name as of primary concern, with carbon dioxide? Answer: Hydrocarbons, oxides of nitrogen and carbon monoxide. Source: US Department of Energy, Alternative Fuels Data Center, Natural Gas Vehicle Emissions, introduction. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), D. Emissions and Performance Verification (11 of 55)
  • The fuel changeover of a bi-fuel vehicle is being checked. How does a bi-fuel engine use its two fuels? Answer: One at a time, switched manually or automatically. Source: Wikipedia, Bi-fuel vehicle, lead section. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), D. Emissions and Performance Verification (11 of 55)
  • Fuel economy is checked in gasoline gallon equivalents (GGE). About how much CNG is one GGE? Answer: 5.66 pounds. Source: US Department of Energy, Alternative Fuels Data Center, Natural Gas Fuel Basics, Compressed Natural Gas. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), D. Emissions and Performance Verification (11 of 55)
  • How does FMVSS No. 303 define a bi-fuel CNG vehicle? Answer: Two independent fuel systems, one for CNG and one for another fuel. Source: 49 CFR 571.303 (FMVSS No. 303, Fuel system integrity of compressed natural gas vehicles), S4, Definitions. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), D. Emissions and Performance Verification (11 of 55)
  • How does FMVSS No. 303 define a dual-fuel CNG vehicle? Answer: A vehicle fueled by two fuels at the same time, one of them CNG. Source: 49 CFR 571.303 (FMVSS No. 303, Fuel system integrity of compressed natural gas vehicles), S4, Definitions. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), D. Emissions and Performance Verification (11 of 55)

System diagnosis, maintenance and repair 15

  • A customer with a dedicated CNG car asks about evaporative fuel losses. What is true of a CNG fuel system? Answer: The fuel system is sealed, so no fuel is lost to evaporation. Source: Wikipedia, Compressed natural gas, Advantages. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), E. System Diagnosis, Maintenance, and Repair (16 of 55)
  • A fill receptacle is replaced with its check valve. What does a check valve do? Answer: Allows flow through it in only one direction. Source: Wikipedia, Check valve, lead section. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), E. System Diagnosis, Maintenance, and Repair (16 of 55)
  • A gasoline car was converted to natural gas and is still under engine warranty. Which oil-change schedule does the Alternative Fuels Data Center say is best to follow? Answer: The original maintenance schedule. Source: US Department of Energy, Alternative Fuels Data Center, Natural Gas Vehicle Maintenance and Safety, Oil-Change Intervals. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), E. System Diagnosis, Maintenance, and Repair (16 of 55)
  • About what voltage does a spark plug usually need in order to fire properly? Answer: 12,000 to 25,000 volts or more. Source: Wikipedia, Spark plug, Operation. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), E. System Diagnosis, Maintenance, and Repair (16 of 55)
  • Before a repair, a technician wants to know which original parts a conversion removed and how the maintenance specifications changed. Where does 40 CFR 85.530 require that to be shown? Answer: On the supplemental emission control information label. Source: 40 CFR 85.530, paragraph (a)(4). Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), E. System Diagnosis, Maintenance, and Repair (16 of 55)
  • How often does the CNG fuel filter generally need to be replaced, by the Alternative Fuels Data Center? Answer: Annually. Source: US Department of Energy, Alternative Fuels Data Center, CNG Fuel System and Tank Maintenance, CNG Fuel System and Tank Maintenance. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), E. System Diagnosis, Maintenance, and Repair (16 of 55)
  • In a single-stage pressure-reducing regulator, what position does the poppet valve take with no inlet pressure? Answer: Open, held by the spring above the diaphragm. Source: Wikipedia, Pressure regulator, lead section and Operation. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), E. System Diagnosis, Maintenance, and Repair (16 of 55)
  • Oil is found in a CNG fuel filter. Where does such oil come from in a gas system? Answer: Lube oil carried downstream from a compressor. Source: Wikipedia, Coalescer, Mechanical coalescers. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), E. System Diagnosis, Maintenance, and Repair (16 of 55)
  • Trouble codes are cleared with a scan tool (OBD service $04) before a road test. What else is erased with them? Answer: The freeze frame data. Source: Wikipedia, On-board diagnostics, Mode of operation/OBD services. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), E. System Diagnosis, Maintenance, and Repair (16 of 55)
  • What does the fuel filter of a CNG fuel system remove? Answer: Oil or contaminants in the fuel. Source: US Department of Energy, Alternative Fuels Data Center, CNG Fuel System and Tank Maintenance, CNG Fuel System and Tank Maintenance. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), E. System Diagnosis, Maintenance, and Repair (16 of 55)
  • Where is the fuel introduced in a spark-ignited natural gas engine, by the Alternative Fuels Data Center? Answer: Into the intake manifold or the combustion chamber. Source: US Department of Energy, Alternative Fuels Data Center, How Do Natural Gas Vehicles Work?, Key Components of a Natural Gas Vehicle. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), E. System Diagnosis, Maintenance, and Repair (16 of 55)
  • Which engine modification does the Alternative Fuels Data Center call typical for a natural gas vehicle? Answer: Hardened exhaust valves and valve seats. Source: US Department of Energy, Alternative Fuels Data Center, Natural Gas Vehicle Maintenance and Safety, introduction. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), E. System Diagnosis, Maintenance, and Repair (16 of 55)
  • Which part of a natural gas vehicle controls the fuel mixture, ignition timing and emissions system, and detects and troubleshoots problems, by the Alternative Fuels Data Center? Answer: The electronic control module (ECM). Source: US Department of Energy, Alternative Fuels Data Center, How Do Natural Gas Vehicles Work?, Key Components of a Natural Gas Vehicle. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), E. System Diagnosis, Maintenance, and Repair (16 of 55)
  • Why does CNG form an even mixture with the intake air? Answer: Being a gaseous fuel, it mixes easily and evenly in air. Source: Wikipedia, Compressed natural gas, Advantages. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), E. System Diagnosis, Maintenance, and Repair (16 of 55)
  • Why does the Alternative Fuels Data Center call it critical to maintain every part of the ignition system of a natural gas engine? Answer: Natural gas is much more sensitive to spark quality and voltage. Source: US Department of Energy, Alternative Fuels Data Center, Natural Gas Vehicle Maintenance and Safety, Ignition Systems. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), E. System Diagnosis, Maintenance, and Repair (16 of 55)

Cylinder safety and maintenance 10

  • A cylinder label reads Type 2, hoop wrapped. Where is the filament wound on such a container? Answer: Around the cylindrical portion of the liner. Source: 49 CFR 571.304 (FMVSS No. 304, Compressed natural gas fuel container integrity), S4, Definitions. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), F. General Cylinder Safety and Maintenance (9 of 55)
  • A solvent spill in a collision may have reached the CNG tank, which shows no dent or scrape. What does the Alternative Fuels Data Center say? Answer: Inspect the tank: certain chemicals can weaken it. Source: US Department of Energy, Alternative Fuels Data Center, Natural Gas Safety after a Traffic Accident, Inspect the Tank. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), F. General Cylinder Safety and Maintenance (9 of 55)
  • A tank reaches its expiration date. Who is responsible for having it replaced, by the Alternative Fuels Data Center? Answer: The vehicle owner or fleet manager: no national system notifies owners. Source: US Department of Energy, Alternative Fuels Data Center, CNG Fuel System and Tank Maintenance, CNG Tank End-of-Life. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), F. General Cylinder Safety and Maintenance (9 of 55)
  • A thermally triggered relief device uses a fusible plug. What makes a fusible plug open? Answer: A set high temperature melts its metal core. Source: Wikipedia, Fusible plug, lead section and Purpose. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), F. General Cylinder Safety and Maintenance (9 of 55)
  • A used CNG tank is bought for a converted vehicle. Technician A says the buyer should verify that enough useful life is left before the expiration date. Technician B says the tank should be inspected by a certified CNG fuel system inspector. Who is right? Answer: Both technicians. Source: US Department of Energy, Alternative Fuels Data Center, CNG Fuel System and Tank Maintenance, CNG Storage Tank Inspection. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), F. General Cylinder Safety and Maintenance (9 of 55)
  • An expired CNG tank has been purged of natural gas. What must happen to it next? Answer: It is rendered unusable and discarded. Source: US Department of Energy, Alternative Fuels Data Center, CNG Fuel System and Tank Maintenance, CNG Tank Replacement. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), F. General Cylinder Safety and Maintenance (9 of 55)
  • An expired tank is taken off a vehicle. Once the CNG is vented, what is the tank purged with, by the Alternative Fuels Data Center? Answer: Nitrogen. Source: US Department of Energy, Alternative Fuels Data Center, CNG Fuel System and Tank Maintenance, CNG Tank Replacement. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), F. General Cylinder Safety and Maintenance (9 of 55)
  • CNG cylinders are removed for service in a repair shop. Which precaution does the Alternative Fuels Data Center name for the cylinders themselves? Answer: Secure them while they are being serviced. Source: US Department of Energy, Alternative Fuels Data Center, Natural Gas Fuel Safety, Compressed Natural Gas. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), F. General Cylinder Safety and Maintenance (9 of 55)
  • How long is the useful life of a CNG fuel tank, by the Alternative Fuels Data Center? Answer: 15 to 20 years, by its construction and certification. Source: US Department of Energy, Alternative Fuels Data Center, CNG Fuel System and Tank Maintenance, CNG Tank End-of-Life. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), F. General Cylinder Safety and Maintenance (9 of 55)
  • Why may a carbon fiber CNG tank take on less fuel than a steel tank in the same fill, by the Alternative Fuels Data Center? Answer: It retains more heat, and warmer gas expands. Source: US Department of Energy, Alternative Fuels Data Center, Filling CNG Fuel Tanks, Tank type. Outline: ASE Compressed Natural Gas Vehicle (F1) Study Guide (2026), F. General Cylinder Safety and Maintenance (9 of 55)

How this list was compiled: Our own questions, written to the six content areas of the test specifications and task list in the ASE Compressed Natural Gas Vehicle (F1) Study Guide (copyright 2026, https://ase.com/wp-content/uploads/ASE_CNGVehicle_Study_Guide.pdf, read 2026-10-14): A pre-service vehicle inspection 5 of 55 scored questions, B CNG system equipment inspection 8, C leak testing and repairs 6, D emissions and performance verification 11, E system diagnosis, maintenance and repair 16, F general cylinder safety and maintenance 9. The bank holds 5, 9, 7, 11, 15 and 10. Every fact was read on 2026-10-14 in the public text the question names: 49 CFR 571.303 and 571.304 (FMVSS No. 303 and No. 304) and 40 CFR 85.505, 85.510, 85.525 and 85.530 at ecfr.gov; the natural gas pages of the Alternative Fuels Data Center of the US Department of Energy (afdc.energy.gov); and Wikipedia articles on compressed natural gas, bi-fuel vehicles, catalytic converters, coalescers, check valves, spark plugs, pressure regulators, fusible plugs and on-board diagnostics. The sample questions printed in the study guide were not used. Licence: Questions, choices and explanations are original work of this site. The Code of Federal Regulations and the Alternative Fuels Data Center are works of the United States government, and no question or example is copied from them.

How it works

This ASE F1 study guide sets out the six content areas of the Compressed Natural Gas Vehicle test and practises each with questions. It is unofficial: the National Institute for Automotive Service Excellence (ASE) neither sponsors nor endorses it.

Read the full guide

The six F1 content areas

ASE's F1 study guide gives system diagnosis, maintenance and repair 16 of the 55 scored questions and emissions and performance verification 11. General cylinder safety and maintenance has 9, CNG system equipment inspection 8, leak testing and repairs 6, and pre-service vehicle inspection 5.

Where the CNG answers come from

Cylinder labels, types and inspection intervals come from FMVSS No. 304 and No. 303. Conversion labels and standards come from EPA's rules in 40 CFR Part 85. Filling, filters, ignition and tank end-of-life come from the Department of Energy's Alternative Fuels Data Center.

What this guide leaves out

ASE's guide says CNG work follows maker guidelines and the current NFPA 52, a privately published code. No question here quotes it; federal rules are asked in its place.

  • Read a cylinder label the way FMVSS No. 304 writes it: type, service pressure, inspection interval and the Do Not Use After date.

Questions and answers

What is the ASE F1 test?

ASE's Alternate Fuels certification test, Compressed Natural Gas Vehicle. ASE's page gives its objective: to recognize technicians who can demonstrate knowledge of the skills necessary to diagnose, service and repair compressed natural gas vehicles.

How many questions are on the ASE F1 test?

Sixty-five, by ASE's 2026 F1 study guide: 55 scored and 10 that do not count, in 90 minutes. The recertification test, F1R, has 28 questions and a 45-minute limit.

Where is the official ASE F1 study guide?

ASE publishes it free as the Compressed Natural Gas Vehicle Study Guide, with the test specifications, task list and six sample questions. This page adds practice on the same content areas; none of ASE's samples is used.

How often is ASE F1 certification renewed?

Every five years. ASE's F1 page says technicians must retest every five years to retain certification, and that the recertification test is about half as long as the first one.

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