Frequently Asked Questions -
Heavy-Duty DECS Installation and Maintenance

This page last reviewed February 3, 2015

What is a verified diesel emission control strategy (DECS)?

A DECS is a technology that reduces harmful air pollution from diesel engine exhaust before it is emitted into the air. The most common technology used as a DECS is a diesel particulate filter (DPF or pm filter) that substitutes for the original muffler. ARB evaluates and approves DECS to meet specific particulate matter (PM) or nitrogen oxide (NOx) emission reductions. Once a device is approved it is considered a “verified” device and may be installed to comply with ARB regulations.

ARB's verification program ensures that emission reductions achieved by a control strategy are both real and durable and that production units in the field are achieving emission reductions which are consistent with their verification. The verification program also requires a minimum warranty be provided by the manufacturer.

Why do I need to install a heavy-duty diesel exhaust retrofit?

Every day on and off-road diesel engines create air pollutants that can adversely affect human health. The ARB requires engine manufacturers to meet strict pollution standards. This means each engine has a limit on the amount of pollutants it can emit. ARB certifies new engines by service class and issues an executive order (EO) that states how the engine is used (on road, off road, etc.) and the emissions limit for each pollutant.
CO2 written in the clouds

Over the years, new engine emission standards have become more stringent, limiting the amount of pollutants that come from diesel engines. New filtration technology has allowed the current generation of diesel engines to emit up to 60 times less pollution than those built 20 year ago. However, because diesel engines last so long, and pollute at much higher rates than is technologically feasible, ARB has implemented regulations to reduce air pollutants from older in-use engines through the installation of either a DECS or by engine replacement.

In order to comply with these diesel regulations, fleet owners may need to install a verified diesel emission control strategy. Make sure you understand what type of DECS, if any, is required to meet the in-use diesel regulations that apply to you, prior to purchasing a DECS.

What are the different types of DECS?

ARB verifies technologies and issues an executive order ensuring that specific levels of engine exhaust emission reductions are obtained. Emission reductions are classified into three "Levels" of particulate matter (PM) reduction and five "Marks" of nitrogen oxide (NOx) reduction:

The “Levels” of particulate matter reduction:
Level 1 - The strategy reduces engine exhaust PM emissions by at least 25 percent.
             Example: diesel oxidation catalyst
Level 2 - The strategy reduces engine exhaust PM emissions by at least 50 percent.
             Example: flow through filter
Level 3 - The strategy reduces engine exhaust PM emissions by at least 85 percent, or
             reduces engine exhaust PM emissions to less than or equal to 0.01 grams diesel
             PM per brake horsepower-hour (g/bhp-hr). Example: wall flow filter

The “Marks” of nitrogen oxide reduction:
Mark 1 - The strategy reduces engine NOx emissions by at least 25 percent
Mark 2 - The strategy reduces engine NOx emissions by at least 40 percent
Mark 3 - The strategy reduces engine NOx emissions by at least 55 percent
Mark 4 - The strategy reduces engine NOx emissions by at least 70 percent
Mark 5 - The strategy reduces engine NOx emissions by at least 85 percent

When an engine is in operation, the diesel particulate filter captures soot inside the filter. As the soot accumulates, the excess soot must be eliminated or burned off through a process known as regeneration. Two major strategies exist for regenerating or burning the soot in the filter: active or passive.

Active Regeneration:
An external source of heat is applied to the filter to raise its temperature to a sufficient level for the soot to be burned off.  This is achieved with either an electric heating element or by injecting fuel directly into the system and igniting it. Regeneration times can vary widely depending on the specific DECS.

Passive Regeneration:
Exhaust temperature is high enough that soot is burned off on an ongoing basis.No outside source of heat is required.

The regeneration strategy required for a specific engine is dependent on the duty cycle of the vehicle or equipment. For passive DPF’s to effectively operate, they must attain a minimum exhaust temperature for a certain percentage of the engine’s operation. The exhaust temperature is dependent on engine design and how hard it works. A duty cycle analysis is typically required to determine if a passive filter is appropriate.

What is a DECS executive order and how do I read it?

Similar to executive orders (EO) for engines, ARB issues EOs for all DECS verifications that contain the requirements that must be met to maintain the verified emission reduction. Disregarding even one of the terms or conditions may lead to problems with the DECS working properly and lead to non-compliance with ARB regulations.

These and other terms and conditions are listed in the DECS EO. Adherence to all of the EO terms and conditions is critical for DECS performance and maintaining compliance with ARB regulations.

Example DECS executive order terms and conditions:
This DECS executive order lists the terms and conditions of a passive DECS for an on-road engine. If you fail to meet any of these terms and conditions you may experience problems with the DECS, void your warranty, or lead to non-compliance with ARB regulations. This EO requires:

1) The engine is originally manufactured from model year 1993 through 2006 having an engine family name listed in Attachment 1.

2) The engine must be used by an on-road motor vehicle with a manufacturer's gross vehicle weight rating of over 14,000 pounds.

3) The engine does not employ exhaust gas recirculation (EGR).

4) The application must have a duty cycle with an exhaust temperature profile greater than 260 C for at least 25 percent of the time.

In this case, this means that over a designated period of time the exhaust temperature must get hotter than 260 degrees Celsius for 25 percent of the time. If it does not meet this temperature the soot will not be burned off or regenerated, and the DECS is not verified for use on this engine.

5) The engine must be in its original certified configuration.

This DECS was designed for an engine emitting PM at its original PM emission level, so if the engine was rebuilt to a higher PM emission level and is now in bad repair resulting in higher PM level, you could experience problems with the DECS, void your warranty or lead to non-compliance with ARB regulations.

6) The engine must not have a pre-existing diesel particulate filter from the original equipment manufacturer.

7) The engine must be certified for on-road applications at a PM emission level of at most 0.1 g/bhp-hr, and greater than 0.01 g/bhp-hr.

An engine with a PM emission level greater than 0.1 g/bhp-hr may produce too much PM for this DECS to regenerate, which will lead to a DECS plugging and potential damage to the device or the engine.

As you can see, there are a lot more terms and conditions listed. Remember that all of the terms and conditions of the DECS executive order must be satisfied in order for the DECS to work properly with a particular engine. The end user is ultimately responsible for complying with the regulations and responsible for the proper installation and maintenance of verified DECS on their diesel engines.

What device must I install?

Diesel engine operators must follow specific regulatory compliance deadlines and requirements regarding the type of DECS installed on each type of vehicle or equipment.

For example, some regulations require the installation of the highest "Level" device, typically known as a "Level 3" DECS. Under this requirement, if a "Level 3" is not available for your specific engine family, a lower DECS can be used. If a lower "Level" DECS is installed, such as a "Level 1" or "Level 2," the end user is responsible to justify the use of a lower "Level" device. Some regulations may only allow "Level 3" DECS and in this instance, if a "Level 1" or "Level 2" DECS is installed, the vehicle will not be in compliance with the in-use diesel regulation because a "Level 3" is required.

To identify the specific regulations that pertain to you please visit the Diesel Programs & Activities webpage or call the diesel hotline at 866-6DIESEL (866-634-3735).

How do I select a DECS?

On every DECS executive order there is a section that lists the terms and conditions that must be met to be installed properly and legally. Using a manufacturer approved installer will help with the selection process, but you should also be aware of these conditions.

Conditions include, but are not limited to, engine type or use (off-road, on-road, transport refrigeration unit, auxiliary power unit, stationary and portable), size of engine (horsepower rating, liter rating, etc.), model year of the engine, fuel use (biodiesel and other additives must be specifically allowed in the EO), engine design (use of engine gas recirculation (EGR) or a diesel oxidation catalyst (DOC)), gross vehicle weight rating of the vehicle, engine exhaust temperature (for passive DECS), PM emission of engine, and others. In addition, each DECS EO provides a list of compatible engines by family name in Attachment 1. EOs are provided on the Verification Procedure webpage at the Currently Verified program links. Ensure that your engine family is verified for the specific DECS you choose to install by reviewing the EO, referencing the ARB's Verification Database or by contacting an installer.

In addition to identification of the approved engine families, maintaining your engine is critical. Engines must be maintained so that it remains within the original manufacturer specifications, including lube oil use and other parameters. Ensure only engine components and fuel used is a part of the original equipment design. Do not add waste oil or additives to the fuel unless approved for use in the EO. If the engine starts using lube oil, PM emissions are increased and can over load the DECS beyond its designed capacity.

For some DECS it is important to maintain normal workload of an engine because it affects the engine's exhaust temperature. Certain DECS (passive) require a minimum engine exhaust temperature in order for the trapped PM or soot to burn off. For passive DECS, if the exhaust does not reach a certain temperature, the device will not regenerate, then clog up, and then possibly damage the device or possibly even the engine.

What do I need to know prior to installation?

ARB recommends that you contact the DECS manufacturer or their authorized installer prior to making any purchasing decisions. Remember, ARB does not recommend specific devices or installers. As with any significant investment, prudent decision making is advisable. In May 2007, ARB issued an advisory (Mail-Out #MSC 07-15) to assist buyers on the proper selection of ARB verified DECS.

The following information is required prior to DECS installation:

1) You must provide the installer the engine family name or emission family name (EFN) and engine model year. An EFN is a string of 10-12 letters and numbers found on the engine's emission control label (ECL) which is attached to the engine. The EFN is required to ensure the DECS is verified for that engine.

For off-road equipment, there are no EFN's for Tier 0 engines (pre-1996) and you should review the off-road frequently asked questions for more information if this applies to you. Most on-road engines have an EFN, however if you have difficulty locating the EFN, contact the engine manufacturer or dealer. Also, pre-1988 engines were not certified to an emission standard, so those are considered unregulated engines.

2) Have the engine in proper working order – the engine must be operating within its original engine specifications. Highly worn engines often smoke more due to high oil or fuel consumption, and therefore do not meet the original engine specifications. If an engine does not meet the manufacturer’s specifications, repairs must be completed prior to retrofitting. Having a poorly maintained engine does not exempt you from complying with the in-use diesel regulations.

3) Ensure the engine meets the terms and conditions listed under ARB's EO verifying the device. The factors outlined in the EO are legal requirements of each verification; therefore, these conditions must be met before determining if a particular device is appropriate.

How much data logging is required before installing a PM filter?

For retrofit filters that have an EO with exhaust gas temperature requirements, the manufacturer or authorized installer must measure and record the exhaust gas temperature for each candidate engine to determine if the temperature requirements are satisfied. The data must be measured and recorded for a period long enough to determine the candidate engine's duty cycle but not less than 24 hours of representative, actual engine run time. For more data logging information, please see Mail-Out #MSC 11-11, Pre-Installation Compatibility Assessment Requirements. PM filter manufacturers may require additional information prior to installation. 

How do I find installers of verified DECS?

The ARB has compiled a list of each manufacturer's authorized installers of verified DECS. Please note that ARB does not endorse, approve, or recommend any of the companies listed herein. The distributors were provided by the device manufacturer. For most updated list of providers, please contact the manufacturers directly.

What must I do after a DECS is installed?

Once the device is installed, the user is required to properly maintain the engine and DECS, and comply with the terms and conditions of the DECS EO.  This includes, but is not limited to, maintaining your engine at the manufacturer's specifications, proper DECS cleaning, proper fuel use, and proper operation of the engine to meet duty cycle requirements.

Typically, depending on various factors, DECS may require annual cleaning of the soot that collects in the filter. A qualified technician using manufacturer approved techniques should perform the operation as the collected soot is considered a hazardous waste and must be treated accordingly. Do not use water sprays or compressed air outside a cleaning machine to clean out a filter.

Increased preventative maintenance and oil consumption tracking is advisable because a DECS potentially captures all visible diesel emissions so looking for the visible sign of a malfunctioning engine is not otherwise possible.

When you purchase a DECS, you should be provided a copy of the DECS warranty, installation warranty, and operation manual. You should know what is required for maintenance of your DECS to keep your warranty valid.

Once the device is installed, the conditions listed in the EO must be maintained. For example, if you change the duty cycle (operational or driving use) of the engine, the engine may not get as hot, causing the exhaust temperature to go below the required value. This would result in operating a non-verified DECS (which does not satisfy regulation requirements), increasing the likelihood of plugging and more frequent cleaning, and potentially leading to damage of the DECS or the engine.

ARB issued an advisory (Mail-Out #MSC 10-41) addressing the necessary steps if a DECS fails and needs repairs outside of the warranty period.

Is the soot considered hazardous waste?

Ash captured by the DECS is considered a California hazardous waste and must be handled appropriately. ARB prepared this guidance document to assist end users who own, operate, or maintain DECS, with respect to managing ash generated by DECS or the disposal of spent DECS.

What is swapping and re-designation?

Swapping is the movement of designated parts between different vehicles/applications within the same common ownership fleet which utilize same PM filters. Swapping is typically used by a fleet to have a “spare” filter available to replace an existing filter when ash cleaning is needed so that the vehicle can operate during the “downtime.” Swapping can only be used within a fleet and between filters of the same family and part number.

is the movement of a used verified PM filter from an appropriate engine/application and installation to another engine/application meeting the terms and conditions of the Executive Order within the same common ownership fleet. Used filters cannot be removed and sold.

Not all DECS manufacturers allow component swapping and/or re-designation. To see if these activities are allowed for your filter, click the filter name on the Currently Verified list. For more information on the swapping and re-designation policy, please see the DECS Component Swapping and Re-Designation Requirements.

Can I put a used PM filter on my vehicle?

Any modification of an engine's certified configuration requires a waiver from California's Anti-Tampering Law, Vehicle Code sections 27156 and 38391. In addition, any component added to an engine to reduce emissions to meet California's in-use emission requirements must be currently verified and installed by a manufacturer's authorized installer. Currently the installation of a filter from one vehicle to another (re-designation) can only occur between vehicles under the same common ownership and the installation meets the manufacturer's ARB approved Swapping and Re-Designation Policy. For more information on re-designation, go to FAQ: What is swapping and re-designation?

A used filter installed from a vehicle not under the same common ownership or outside of a manufacturer's approved swapping and re-designation policy, is a violation of California's Anti-Tampering Law, Vehicle Code sections 27156 and 38391.

What do I do if I have a complaint about a DECS?

DECS owners who have problems with their system should first contact the installer. The installer should be able to assist with diagnosis and repairs as well as provide warranty work, if available. If the installer is unable to provide service to your satisfaction you should contact the manufacturer of the DECS. Manufacturers have a unique understanding of your system’s operation and can often assist with malfunctioning products. If you feel that there is a serious problem with your DECS and, after contacting the installer and manufacturer, you may contact ARB. Inquiries should be addressed to the specific regulatory program that the equipment is compelled to comply with.