There are very few CNG vehicles available from the factory. The big three American auto makers used to offer CNG (and LPG) vehicles at one time but for various reasons no longer offer them. Honda makes the Civic GX, which is CARB-certified.
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On an aftermarket basis, the CNG conversions available in North America are:
The reason that so few EPA or CARB certified systems are available is because of the extremely low demand for these products. All EPA and CARB certified conversions start off as universal conversion kits. Once vehicle-specific components (like brackets and interfaces) are developed and the controller is configured with vehicle-specific programming, a vehicle is then tested in an emissions laboratory to verify that it meets regulatory requirements. Although there is a fee for the certificate, it is the cost of the lab testing that adds significantly to the cost of a certified conversion.
The cost of obtaining EPA-certification can easily be $100,000 or more and these certifications are model and year-specific. The added cost of the certified system over the cost of the universal system reflects the amortized cost of the EPA certification along with the cost of the additional vehicle-specific components. For example, if the manufacturer expects to sell 100 units per year, EPA certification costs $100,000, and the additional components cost $500 per kit, an EPA-certified kit can easily cost $1500 more than a universal system in order for the manufacturer to break even on this investment. These certifications have a 1-year lifespan so the manufacturer must obtain a new certificate every year. Not only that, generally only new vehicles are converted for fleet applications so the sales of particular certified system will progressively decrease every year because older vehicles are generally not converted to CNG. Typically, Technocarb requires a minimum order of 100 vehicles to create an certified conversion kit.
Therefore, the low demand for certified systems is in response to their high cost. Prior to obtaining certification, the manufacturer must also invest in research and development of components and programming for that one particular vehicle platform. CARB certification could easily be double the cost of EPA certification. Very few people or businesses are ready to spend this extra money so very few certified conversions are on the market.