FREQUENTLY ASKED QUESTIONS (FAQs)

Skyline Emissions

Where can I buy Skyline DPFs, DOCs, sensors, gaskets, and clamps?

Skyline DPFs, DOCs, clamps, gaskets, and sensors are sold, installed and supported through a network of distributors across North America. Contact Skyline to find the distributor in your area.

Who is Skyline Emissions?

Skyline Emissions’ mission is to build high quality, cost-effective aftermarket diesel particulate filters (DPFs) and diesel oxidation catalysts (DOCs). With a new state-of-the-art facility, Skyline is poised to meet the demand for aftermarket DPFs and DOCs. The Skyline video is a good introduction to what Skyline does.

ESW Group is a company with many years of experience in diesel engine emissions control and engine and vehicle testing.

Under the brand ESW Group, we produce retrofit emission control systems for on and off-road diesel engines, with over 20,000 installations around North America. Our products are supported by a knowledgeable and experienced engineering, service, and warranty teams.

ESW America conducts engine and vehicle performance and emission testing at its Montgomeryville, Pennsylvania facility, with eight test cells for engines and vehicles between 20 and 1000 hp (15 to 750 kW).

Skyline Advantages

Why should I choose a Skyline DOC or DPF product over others?

Skyline DOCs and DPFs are designed to be direct replacements for parts from the original equipment manufacturer (OEM), with exact fit geometry. Using OEM-grade substrates and coatings, Skyline provides performance equivalent to the OEM part. In addition to complying with emissions regulations, the Skyline DPF has demonstrated passive regeneration performance 50% greater than some other aftermarket products. It is more efficient, it will last longer, and if properly maintained, you will experience fewer warning lights. Essentially, Skyline DOCs and DPFs are designed to keep your truck in service.

How does backpressure compare between Skyline and OEM?

DPF backpressure is an important performance characteristic. High backpressure can increase fuel consumption and shorten the lifetime of the DPF. The Skyline DPF is designed to be an exact replacement to the OEM part, including backpressure. ESW has extensively tested the Skyline DPF in our emissions testing facilities and in the field to ensure that the backpressure performance is equivalent to the OEM product. You can be assured of OEM level performance on every Skyline DPF, as we use only established OEM suppliers for our DPF products.

Product Coverage

What model year range does Skyline DPF and DOC products cover?

Skyline DPFs and DOCs are available for a wide variety of 2007 and newer on-road diesel engines. The current availability is listed on the website, or in cross-reference files that are available from a Skyline sales representative.

Can I use a Skyline DPF or DOC in California?

No. Skyline products are not approved for sale, installation, or use in California. Violators could be cited by state vehicle inspectors.

Buying Skyline Products

Where do I find the Skyline parts I need?

The most direct way is to enter the OEM part number in the search field on the Skyline website to find the correct replacement Skyline DOC, DPF, clamp, gasket, or NOx sensor. Or, you can try searching by engine model or by browsing the collection. Contact your Skyline distributor if you need assistance.

Does Skyline have minimum order quantities?

Skyline has no minimum order rules, but your local distributor might. Contact us to find the distributor in your area.

Can I order online?

Only distributors can order online. If you are not a distributor, Skyline products are sold, installed, and supported through a network of specialized distributors across North America. Contact us to find the distributor in your area. Distributors have access to our online web portal.

If you are interested in becoming a Skyline distributor, contact Skyline for more information.

Does Skyline sell replacement parts for retrofit DPF systems?

No, but its associated division ESW Group does. Visit the ESW Group website for more information about CARB-verified retrofit systems and parts.

Warranty

What is the warranty on Skyline DPF or DOC products?

Skyline DPFs and DOCs are backed by a 3 year, unlimited mileage warranty.

Who do I contact about warranty questions??

Contact a Skyline distributor or consult your owner’s manual. If you still have questions that have not been answered, email us here.

How do I register my Skyline product for warranty?

No registration is necessary. Your proof of purchase — the receipt from the Skyline distributor — is your warranty card. The start date for the warranty period is the date of purchase.

Maintenance

Why does my DPF require periodic maintenance?

Fuel and oil contain inorganic additives to help protect your engine and extend the life of the oil. During the combustion process, they are turned into ash, which collects in the DPF over time. Unlike the black carbon in the exhaust, which is removed during the regeneration process, the ash can only be removed by a cleaning device. This requires the DPF to be removed from the engine. The cleaning interval varies for each engine manufacturer (and sometimes between engines from the same manufacturer) and can be found in your vehicle’s service guidelines. You should follow the engine manufacturer’s recommended cleaning intervals for your Skyline DPF just like you would for the original DPF.

Note that the amount of ash is directly related to the amount of oil an engine consumes. High oil consumption or high hours of service means more ash in the DPF and may require more frequent cleaning.

How do I maintain a Skyline DPF?

The Skyline DPF is designed to be an exact replacement to the OEM part, so you maintain the Skyline DPF just like you maintain the OEM DPF. Refer to the OEM service documents for instructions and cautions.

Where can I get my DPF cleaned?

A network of DPF cleaning services has developed since DPFs became standard equipment on trucks and buses. Some Skyline distributors also have cleaning services, so your Skyline distributor would be a good starting point to find a reliable cleaning service.

Can I use my own DPF cleaning machine?

If a filter cleaning machine is approved by the OEM, it can be used to clean your Skyline DPF.

Does a Skyline DOC require periodic maintenance?

No, unless DOC maintenance is specifically called out in your engine’s maintenance instructions.

DPF and DOC Technical Topics

Why do some of Skyline's recent DPF releases look different than the earlier DPFs?

In recent years, some OEMs have started to use a different type of DPF material in their heavy-duty aftertreatment systems. Since Skyline matches the OEM design, our DPFs use the same type of filter material.

These DPFs are made from a material called Silicon Carbide (sometimes abbreviated as SiC, its chemical formula). It differs from the more common material (cordierite) in color and how the filter is assembled. Silicon carbide is dark gray and the DPF is almost always a collection of smaller pieces that are cemented together, often in a checkerboard pattern. In contrast, a cordierite DPF is typically tan and built as a single continuous cylinder. The photos below illustrate these differences.

Unless the OEM specifies otherwise in their service documents, a cordierite filter must always be replaced by a cordierite filter, and a silicon carbide filter replaced by a silicon carbide filter. Although both DPF types provide nearly 100% PM reduction efficiency, the OEM’s regeneration strategy and fault codes are designed around a particular material, so switching material without OEM authorization could cause undesirable effects.

Why is engine maintenance important?

A poorly maintained engine lowers your fuel economy, increases emissions, and shortens the life of your engine and emissions critical components such as the DPF and DOC. Deferred or neglected maintenance items may include the following: restricted air filters, stuck EGR valves, faulty fuel injectors, faulty turbochargers, and degraded charge air coolers.

Regular vehicle, engine and after-treatment maintenance (including the DPF), will yield more vehicle “up time,” with reduced operating costs, and maximize your return on the investment that you made in the vehicle.

What does passive and active regeneration mean?

As an engine runs, the DPF collects solid particles called particulate matter (“PM”) which consists of carbon, unburned fuel and oil, the ash from fuel and oil additives, as well as any other contaminants from the exhaust. Over time, the DPF will fill with PM. The process of removing the combustible part of the PM (the carbon, unburned fuel, and unburned oil) is generally called “regeneration.”

Under driving conditions with the engine producing high exhaust temperatures — on a highway or pulling a heavy load — the catalytic coatings on the DPF and DOC are sufficient to keep the DPF clean. This cleaning process that takes place without any activity by the engine is called “passive regeneration.”

When the exhaust temperature is not sufficiently high, the vehicle’s exhaust system relies on auxiliary fuel injection to raise the temperature of the DPF to a level at which the most of the PM is oxidized. This process is actively controlled by the engine‘s controller and therefore called “active regeneration.” The active regeneration occurs periodically and is not noticeable to the driver. Numerous sensors on the engine and exhaust system provide input to the engine‘s controller so it can trigger and control the process.

Most engines have another type of active regeneration that is initiated by the operator when the vehicle is standing still. This process is called "stationary regeneration" or "forced regeneration." During the process, the engine controller modifies the engine speed, intake air flow, EGR rate, and other functions to allow the DPF temperature to reach a suitable temperature. Consult your engine or vehicle owner's manual for details.

In most cases your vehicle relies on both passive and active regeneration to keep the DPF clean and the vehicle operating normally.

Why is it not good to idle the engine for long periods?

Extended periods of idling shorten the lifetime of your engine, consume fuel unnecessarily and load up the DPF . In addition, some states, private entities (like warehouses or loading docks), and many municipalities have strict anti-idling laws or policies.

Why does the surface color of DOCs and DPFs vary for different pieces?

The color varies because the raw materials used by catalyst coating companies can vary for different production lots. Skyline's catalyst supplier has strict quality requirements for all of their raw materials in terms of material, particle size, but not color, so that is one source of the surface varying in shade.

Why do some DOC and DPF surfaces have patterns of color like coffee cup stains and other shapes?

Catalyst coatings are wet — slurries of small particles and water — so the parts are dried after coating. Sometimes the inlet or outlet surfaces might have uneven dispersion of material

NOx Sensors

NOx Sensor Product Information

What is the NOx in “NOx Sensor”?

NOx is a gas that is also known as ‘nitrogen oxide’ and ‘oxides of nitrogen’ (some companies, like Cummins, use the term in their on-line catalogs). It is not a single molecule, but a blend of nitric oxide (NO) and nitrogen dioxide (NO₂). These two molecules are one of the main causes of urban smog and health hazards in their own right (especially NO₂).

What is the difference between Skyline’s SNX and ANX sensors?

The SNX sensors are "OE-Manufactured" sensors that are built by the suppliers to the OEM and made in the USA. Because these emissions-related parts are built by the OEM suppliers to exact OEM specifications, they are OK to sell and use in California.

The ANX sensors are built by an aftermarket specialist that also does some work for OEMs. The ANX sensors cannot be sold or used in California.

Both lines of sensors are built with all-new materials, don't have a core charge, and have warranty of 1 year.

I have two sensors with different part numbers that have identical appearances. Can I substitute one for the other?

No, NOx sensors are a smart sensor with specific programming. If you install the incorrect part number it might result in a check engine light. If you have a check engine light immediately after install the first step is to make sure you installed the correct part number.

What does the NGK marking on the Skyline OE-Manufactured sensor head mean?

It means that the sensor head was built by NGK, one of the companies that invented the NOx sensor and supplies the OEMs with sensor head technology. NGK sensor heads are generally thought of as the best.

What is the “Continental number” that I keep hearing about?

Most OEM part numbers for heavy-duty NOx sensors have an associated “Continental number” because Continental is one of the major manufacturers of NOx sensors. For example, Cummins 4326864 is connected to Continental number 5WK9 6749B. Skyline tries to include the Continental number in the cross-reference lists on the website.

Why should I buy my NOx sensors from Skyline instead of one of the bargain sellers on Amazon?

Skyline has gone through an extensive vetting process of aftermarket NOx sensor manufacturers, working directly with them, getting information from their engineering department, and performing tests in our engine test laboratory when feasible. Furthermore, Skyline has a long track record in the diesel emission control field, a 1-year warranty, and will be there if you have trouble with the NOx sensor, while Amazon sellers come and go.

Why has the packaging for the ANX sensors changed?

Our sensor manufacturer previously used an anti-electrostatic-discharge bag for sensor packaging, but has recently changed the packaging to paper. They found that it did not benefit the sensor’s performance or durability, and a paper wrapper would make it easier to access the part (no scissors or knife needed) and be fully recyclable. Several OEMs ship their sensors with similar packaging.

Why do some Skyline NOx sensors have shiny heat wrap?

Some of the OEMs, notably Cummins, have started shipping new and remanufactured NOx sensors with a heat wrap to provide extra thermal protection on the wiring harness. Skyline has started ordering aftermarket sensors with heat wrap, so you'll see them on certain ANX NOx sensors going forward.

I want to put the shiny heat wrap on a NOx sensor or provide the wrap to my customer. Does Skyline sell it?

Not at this time, but we are considering it. Contact Skyline if you are interested.

NOx Sensor Operation

What does a NOx sensor do?

The inlet NOx sensor measures the concentration of NOx exiting the engine, which is used to determine the amount of DEF required for effective NOx reduction in the SCR. The outlet NOx sensor measures the NOx levels leaving the SCR to verify proper system performance.

Where are NOx sensors located?

The inlet NOx sensor is located somewhere upstream of the SCR inlet, while the outlet NOx sensor is positioned at the SCR outlet. Although exact locations may vary by application, the inlet sensor is always upstream of the SCR and the outlet sensor is always downstream.

What are the main components of a NOx sensor?

The main components are shown in the illustration below:

1. Sensor-head harness: the electrical connection between the sensor head and the electronic module that provides power, ground, a voltage-signal line (“start”, “stop”, and so on), and a voltage-output line for the sensor head.
2. Harness connector: the connection point for the sensor-head harness. Do not disconnect this.
3. Electronic module: This is the circuit board that reads the sensor output and communicates with the engine using the CANbus
4. Sensor head: the sensor head contains a ceramic sensor and other hardware that can detect the NOx concentration in the exhaust gas, as well as hardware that provides heating, cleaning, and communication.
5. Receptacle on the module: this is where the harness from the engine control unit connects. There are a variety of shapes (oval, oblong) and typically 4 pins (power, ground, CAN high, CAN low).

What can go wrong with NOx sensors?

NOx sensors live in a harsh environment including stressors like diesel exhaust, high temperatures, road debris, and salt spray. Some of the most common issues for NOx sensors are installing the incorrect part number, OEM software updates causing false codes, contamination by excessive soot, excessive unburned fuel, moisture to the connector or the sensor head, coolant contamination from a leaking EGR cooler, or DEF crystallization from a leaking DEF doser; electrical issues like broken connections; and communication errors caused by damage to the CAN bus wiring.

Why do NOx sensors have such a bad reputation?

There are several reasons for this. The top two are 1) NOx sensors work on the CAN bus (a.k.a. the J1939 network), and therefore need to communicate using the OEM's "language". Aftermarket products can have problems getting that communication right. 2) NOx sensors are doing a difficult job, measuring a very small quantity of gas in a dirty and hot exhaust stream. 3) Improper or incomplete troubleshooting. Just because you have a NOx sensor code, it doesn’t mean the NOx sensor has failed.

Does it make sense to replace the inlet and outlet at the same time?

Other aftermarket companies suggest this but it is not recommended by the OEM therefore it is not required. If the engine has high mileage and both NOx sensors are original you may consider replacing both when one fails to prevent future downtime. Leave this decision up to the owner of the truck.

Is NOx the same as Nitrous Oxide?

No, they are different chemicals and have different health and environmental impacts.

Although nitrous oxide is indeed emitted by diesel engines, the pollutant of concern is nitrogen oxide. Also known as ‘oxides of nitrogen’ or more commonly NOx, it is not a single molecule, but a blend of nitric oxide (NO) and nitrogen dioxide (NO₂). These two molecules are the primary nitrogen-containing precursors to urban smog and health hazards in their own right (especially NO₂). In the lower atmosphere, they go through a complex set of reactions with sunlight and other pollutants to form ozone and the other harmful gases that are normally called “urban smog”.

Nitrous oxide (N₂O) is relatively harmless to humans — as evidenced by its use in dental and medical offices — and has little smog forming potential. It is emitted by engines in far smaller quantities than NO and NO₂. Despite its benign nature, nitrous oxide is several hundred times more effective than carbon dioxide at keeping heat within the atmosphere, and is thus a greenhouse gas of concern.

Deborah Lockridge, writing at Heavy Duty Trucking has a good explainer of NOx versus Nitrous.

Replacement

Should the threads of a new sensor head be treated with any products?

For a new sensor, the manufacturer has applied the right amount of anti-seize compound, do not remove it or add additional product. However, if you are installing a functional used sensor on an exhaust system, use a small amount of anti-seize on the threads.

What is the recommended torque for the sensor head and mounting bolts?

Our manufacturers recommend 50 ± 10 N·m (37.5 ± 7.5 ft·lb) for the sensor head. For the torque on the mounting bolt nuts, follow the engine OEM’s recommendation, as those parts are supplied by the engine manufacturer not the sensor manufacturer.

What are some best practices for NOx sensor removal and installation?

Removal

• Shut off the engine, apply parking brakes, and disconnect the batteries before starting the sensor removal.
• If the removed sensor head looks clogged, be sure to check for engine or aftertreatment faults. Some of the main causes of sensor clogging include poor engine operation, poor DEF system performance (especially DEF injection and mixing), and elevated backpressure over long periods of time. A throttle snap test can be done to confirm if there is excessive black smoke exiting the engine.

Installation

• Do not spray the sensor with chemicals (cleaners, paint) or compressed air.
• Do not disconnect the parts of the sensor.
• The sensor head contains a ceramic chip that could be damaged by a sharp blow or drop. If the new sensor has been dropped or struck after removal from the box, do not use it.
• Take care to avoid electrostatic charge.
• The sensor has the correct amount of anti-seize compound, no additional is needed.
• Torque the sensor head to 50 ± 10 N·m (37.5 ± 7.5 ft·lb). Mounting bolt nut torque is supplied by engine OEM.
• When mounting the cable, maintain strain relief (slack) and avoid dangling wires that could be snagged by road debris or other hazards. If wire ties are used, make sure to use the correct type to avoid rub throughs.
• Review fault codes using a scan tool: clear inactive codes as needed, take action on fault codes that could have caused a NOx sensor issue (injector problems, regen problems, DEF system malfunctions).
• When performing a functional check, remember that NOx sensors have a warm-up time of 5 to 10 minutes, so allow enough idle time before checking the readings.