Get our FREE Newsletter
Name :
Email :
Company :
Frequently Asked Questions About Converting Vehicles to Operate on Natural Gas
Natural Gas Vehicles for America  (

The rising cost of gasoline and diesel fuel is prompting many people to investigate options to retrofit (“convert”) their car or pick up truck to run solely on natural gas (referred to as “dedicated”) or to run on gasoline or natural gas (referred to as “bifuel”). This document answers the basic questions most often posed to NGV America about this topic including: conversion system availability, installation, service and warranty issues, costs and available tax credits.


Installation of an engine conversion package and fueling system may be done after the vehicle has been in service or when the vehicle is first purchased. EPA and CARB require that SVMs provide appropriate documentation and training to installers of their system, commonly referred to as “qualified system retrofitters” (QSR). Installation by a non-qualified installer could damage the retrofit equipment or the engine (or both), compromise vehicle performance, or render the vehicle unsafe to operate.

No EPA or CARB certified engine conversion systems are sold to untrained/unapproved installers. This is not a “kit” you buy and install in your own garage or have installed by the local untrained mechanic. Some SVMs prefer to install their systems themselves at their corporate facilities while other SVM s choose not to install their own equipment- opting instead to sell their systems only through QSRs. Typically, the QSR is responsible for obtaining the fuel storage system components (cylinders, high-pressure tubing, pressure release device (PRD), brackets, protective plates, etc.) and installing these components in accordance with the National Fire Protection Association’s (NFPA) Vehicular Fuel Systems Code (NFPA 52).

Service and Warranty Issues

Generally, vehicle warranties offered by the original automotive manufacturer (OEM) are not affected by the installation of an engine retrofit system, with the exception that the engine warranty for all items related directly to the retrofit system which will now be covered by the SVM. The OEMs warranty on non-engine-retrofit-system-related items (e.g., a defective lock, leaking power steering pump) remains in force. Many OEM dealers are unfamiliar with NGV retrofit systems and logistics, and may errantly tell customers that the “vehicle warranty” will be voided, but this is inaccurate. Courts have upheld the OEM’s non-engine-retrofit-system-related warranty obligations.

Because natural gas engines work essentially the same way as gasoline engines – i.e. an air-fuel mixture is injected into the head or directly into the combustion chamber and ignited by a sparkplug – most engine service issues are very similar and can be handled by the OEM dealer or local automotive service shop. These include oil changes, air filter changes etc. If and when a retrofit system-related service issue arises (e.g., a faulty injector or loose compression fitting), the SVM usually recommends that a QSR perform this work, or, in the case of the SVM that installs the system themselves, a local SVM trained OEM dealer or automotive shop will be recommended.

Occasional inspection of all vehicle systems is generally good practice, regardless of the fuel type. NHTSA, the federal agency with jurisdiction concerning vehicle safety, requires that all CNG fuel storage cylinders have a label that (1) states the date of manufacture and the date that the cylinder is required to be removed from service (typically 15-20 years), and (2) instructs the vehicle owner/operator to have a qualified visual inspection of the tank every 36,000 miles or every 3 years (whichever occurs first) and/or after an accident or fire. Converters and vehicle owners should have documentation that this safety inspection has been done. Inspections are performed to look for tank and bracket damage (e.g., gouges, cuts, abrasions, dents, corrosion, rust, general wear, etc.). Qualified cylinder inspectors are located throughout the US and Canada. The cost/time associated with a cylinder inspection is minimal. More information about CNG cylinder inspections and links to certified inspectors is available at Always check with the SVM and/or the QSR concerning recommended service practices and warranty coverage.

EPA and CARB Certifications

To obtain EPA and CARB certification for a specific engine or engine family, manufacturers of retrofit systems (referred to as Small Volume Manufacturers – SVM) must submit a converted vehicle to EPA or CARB for rigorous testing along with substantial technical documentation. This testing assures that the retrofitted vehicle meets the same stringent emissions requirements the original equipment manufacturers (OEM) -- e.g., GM and Ford – met when they submitted their gasoline or diesel powered vehicle for certification. The testing also ensures that the retrofit system works seamlessly with the OEM’s on-board diagnostics (OBD) system to indicate when emissions are outside of approved parameters and to log those anomalies in the computer memory for downloading by the automotive service technician. Non-certified systems usually do not meet this important criterion and will fail state or local emissions tests. The process of engineering, manufacturing, installing, pretesting and then submitting a proposed retrofit system to an EPA or CARB-approved laboratory for certification is a time-consuming and expensive process that may cost as much as $300,000 or more per engine family. SVMs recoup this R&D investment by amortizing the cost across the expected sales volume, adding it to the price they charge for the various components (computer control module, regulator, injectors, high pressure hoses and fittings, etc.).

Why do Conversions have to be EPA approved?

The Environmental Protection Agency (EPA) has rules concerning the manufacture, sale and installation of alternative fuel engine conversion systems. In California, similar and even more stringent emission rules and guidelines have been established by the state’s Air Resource Board (CARB). As allowed under federal law, some states have adopted or have announced they will adopt the CARB guidelines. These include: Arizona, Colorado, Connecticut, Florida, Maine, Massachusetts, Maryland, New Jersey, New Mexico, New York, Oregon, Pennsylvania, Rhode Island, Utah, Vermont, and Washington. These rules apply to both natural gas and propane powered engine retrofit systems, and will presumably apply to ethanol and/or hydrogen retrofit systems if/when they are ever approved. Only EPA and/or CARB certified conversion systems are permitted to be installed on vehicles manufactured since 1994 (when EPA first addressed the issue of conversion systems). [Per EPA directive concerning conversion of vehicles manufactured prior to 1994, the owner/installer should not do anything that they believe - using reasonable judgment – would diminish the vehicles emissions performance – See EPA’s website for further clarification on this issue]. While a variety of non-certified systems are sold on the Internet and/or offered by some automotive shops, EPA has taken the position that installation of these systems is “tampering with a federally approved emission control system”, a federal violation punishable by a substantial financial penalty (more than $5000/day). Many of these non-certified systems are allowed in other countries that have less strict vehicle emissions and safety laws.


Follow these links to learn more about CNG

For more information on our current projects, please email us at

Linked in