Truck engines are required to have diesel particulate filters (DPFs) to comply with California's fleet rules.  If you are looking to purchase a truck that is advertised as "compliant," make sure that a filter is present and not broken.  Filter cores cost several thousands of dollars and are required to meet the engine or verification approval to be legal to operate.

If your truck engine does not have a diesel particulate filter (2006 MY or older engine), you can only retrofit the engine with a device that has been verified to reduce emissions by ARB to comply with the in-use regulations (see Diesel Emission Control Strategy (DPF) below).  Be aware that some companies are advertising and attempting to sell devices or used DPFs that may not qualify for credit toward compliance with Air Resources Board (ARB) in-use diesel engine regulations.  Used DPFs cannot be sold for re-installation on another vehicle.

Just because a device has an ARB Executive Order (EO) does not mean it is approved for all uses.  ARB mobile source program issues EOs to manufacturers to allow for the sale, use or installation of engines, engine parts, or equipment to clean-up engine emissions. Each EO provides an approval for a specific program, not all programs.  For example, a device that has approval as an aftermarket part only has a waiver from California's anti-tampering law, Vehicle Code Section 27156

Aftermarket parts do not qualify for credit toward compliance with ARB's in-use diesel engine regulations.  Below is an explanation of ARB's approval process through the issuance of an Executive Order or EO and examples of EOs used in specific programs that are important to the heavy duty diesel in-use regulation compliance.

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What to look for when buying a used vehicle
When purchasing a "CARB compliant" used vehicle, be sure to confirm the OEM filter (2007 or newer engines) or retrofit filter is present and working correctly.  To ensure the vehicle meets ARB requirements, have it inspected before purchase by the engine dealership or authorized installer (if it is a retrofit).  If your PM filter core is cracked or missing, it can cost you thousands of dollars and violate California's anti-tampering law, Vehicle Code Section 27156 (VC 27156).

What is an Executive Order or EO?
Executive Orders (EOs) are used where regulations require Executive Officer approval.  ARB conducts a wide range of activities that require Executive Officer approval, therefore EOs are issued for multiple programs. A list of programs that utilize EO approvals can be found at The fact that a particular engine or engine part is approved by ARB and has an EO does not necessarily mean that the engine or part is legal for all uses. Each program EO is uniquely identified for the program it is issued.

Diesel Emission Control Strategy (DPF) Verification
ARB introduced the diesel emission control strategy as a way to reduce emissions from existing older in-use diesel engines. Many in-use regulations require the addition of these strategies to reduce emissions from existing in-use engines. Common names for these strategies are retrofit filters, soot filters, diesel particulate filters, DPFs, and many others.  These filters are considered aftermarket parts, and they are verified to reduce emissions. A manufacturer designs and tests a device to reduce emissions and submits the design and testing information for approval. ARB issues an EO after a product is verified to reduce the stated emissions. These EOs direct the operating conditions, type of engine, and the way the product can be used. You as a consumer should understand the requirement of the EO because operating outside of the requirements void the anti-tampering waiver leading to non-compliance with California's anti-tampering law, Vehicle Code Section 27156. To know if a product is verified under the diesel emission control strategy or verification program, get the EO number of the product. If it starts with "DE", it is a diesel emission control strategy. Before purchasing, always check the "Currently Verified" webpage to confirm if a product is currently verified and approved for installation on your engine for compliance with in-use diesel regulations. Also, use a manufacturer authorized installer to ensure the product is installed properly and meets the EO requirements.

Diesel Emission Control Strategy Verification Program (Currently Verified) (Example)

Engine Certification
Engine and vehicle manufacturers design and test equipment to meet specific emission standards (or limits) for a variety of pollutants. ARB issues an EO to certify that the engine design meets these requirements. Each engine design is issued an engine family name by the engine manufacturer and submitted to ARB for certification for use for a specific service class (i.e. heavy duty, medium-duty, off-road). ARB issues an EO which allows that engine to be sold and operated in California. An engine emission control label (ECL) is required on engines that provide the engine’s emissions information (such model year or tier level and family name). If you are buying a new product and do not have access to the ECL, you can look up the EO issued for certification of the engine and it will have this information. EOs issued for heavy-duty on-road engines start with the letter "A". EOs issued for heavy-duty off-road compression ignition engines start with the letters "U-R".

On-Road New Vehicle and Engine Certification Program (Executive Orders) (Example)

Off-Road Compression Ignition Engine Program (Executive Orders) (Example)

Aftermarket, Performance and Add-on Part Certification
California’s anti-tampering law, Vehicle Code Section 27156 (VC 27156), prohibits the modification or use of parts on an engine other than the original manufacturer's parts. To use a non-original manufacturer part or add on new parts outside of how the engine designed and certified, requires an "anti-tampering" waiver. There are many engine performance products on the market that manufacturers must demonstrate to ARB that do not increase the certified emission levels of that vehicle or engine prior to the offer for sale or installation on an engine. ARB approves the use of these products through issuing an EO that certifies the part “does no harm” to the emission level of a specific engine. The EO contains requirements to ensure that no emission increases occur from the original engine certified configuration. These products are not approved by ARB to reduce emissions, but have an anti-tampering waiver to be used as a replacement or add-on part. You as a consumer can know the difference between an aftermarket part and one that is approved to reduce emissions by obtaining the part EO number. If it starts with a “D”, it is an aftermarket part and is not verified to reduce emissions – no matter what the salesman tells you!

Aftermarket, Performance and Add-on Part Program (Executive Orders) (Example)