Guide to Available Natural Gas Vehicles and Engines

On the following pages, NGVAmerica has assembled information about vehicles and/or engines that have been certified by the US Environmental Protection Agency (EPA) and/or California Air Resources Board (CARB) to operate on natural gas, either as (1) dedicated vehicles - spark-ignited engine operates on natural gas only , (2) bi-fuel vehicles - spark-ignited engine operates on either compressed natural gas (CNG) or gasoline, but not both at same time, or (3) dual-fuel vehicles - compression-cycle engine operates primarily on natural gas but uses diesel as ignition "pilot".*
Generally, CARB's certification procedure imposes more testing and documentation requirements for both new-vehicle and aftermarket engine retrofit ("conversion") systems than EPA, although both CARB and EPA have similar emissions and on-board diagnostics (OBD) compliance requirements. Other differences between the two sets of standards is that EPA classifies vehicles under 8500 pounds GVW as light duty and those over as heavy-duty while CARB's light duty classification goes up to 10,000 pounds. While most states require only EPA certification of new vehicles and aftermarket retrofit systems, a growing number of states are opting to adopt CARB standards for sale and/or registration of new vehicles. Check with your state officials to determine whether CARB standards for aftermarket retrofit systems have been adopted in your state; otherwise EPA standards apply.
This Guide's list of light -duty vehicles includes those manufactured at the factory by traditional Original Equipment Manufacturers (OEMs) such as American Honda, and those retrofit with EPA- or CARB-certified engine systems after leaving the factory using systems made by Small Volume Original Equipment Manufacturers (SVMs). Furthermore, SVM engine retrofit systems may be installed before placing the vehicle into active service or afterward. System installations are usually handled by the SVMs themselves or their Qualified System Retrofitters. Note that, unlike the unregulated "conversion kits" that were available from dozens of manufacturers in the late-1970s through the mid-1990s, all gaseous fuel engine systems on the market today are engineered and tested to comply with the same tough CARB and/or EPA emissions performance requirements as the large automobile manufacturers.
Also note that EPA and CARB certifications of light-duty vehicle retrofit systems are for specific model years and installation time-periods. Only ACTIVE CERTIFICATIONS are listed on the chart starting on page 3. Some SVMs also hold certifications from previous years but these may not have been "carried forward" as required by EPA if the installation time period for the model year for which the cert was issued has now passed. Those interested in converting an existing vehicle should check with the SVMs about whether these prior year certifications have been renewed. Most have not been carried forward more than a year or two from the original model year in which they were issued.

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