Jun. 23, 2025
Automobiles & Motorcycles
In , an investigation conducted by the Washington State Fire Department linked a truck's DPF failure to one of the biggest fires in the state. Over 3,600 acres of land burned, destroying over 100 buildings, including homes. While the cause of the DPF's demise wasn't determined, all too often these kinds of dangerous failures start with—or are exacerbated by—serious diesel oxidation catalyst problems.
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Don’t let that kind of breakdown happen to you. Instead, learn what causes DOC failure, and take steps to prevent it. Or, at least, mitigate the worst of its effects.
A diesel oxidation catalyst (DOC) is similar to the catalytic converter in a car's engine. It cuts down on harmful emissions by transforming toxic particles in diesel engine exhaust through chemical reactions. It also increases the concentration of NO2 in the diesel particulate filter to facilitate DPF regeneration.
Coated with rare metals, DOCs scaffold and enact a chemical reaction. They convert carbon monoxide (CO), hydrocarbons (HC), and other particulate pollutants in exhaust (diesel engine waste) into carbon dioxide (CO₂), water vapor, and nitrogen dioxide (NO₂)—all safer outputs.
A warning light should turn on if a truck’s DOC is losing functionality. But, other signs might grant an earlier warning. Look for:
Reduced fuel efficiency
An increase in exhaust smoke volume (particularly white smoke)
Frequent DPF regeneration cycles
Increased engine heat
DOC failure requires swift attention. Fortunately, not every cause is equally challenging to resolve. When a DOC malfunctions, there are five usual suspects.
“Soot” is the informal term for the solid particulates and hydrocarbons the DOC chemically converts. But, even though it runs continuously, the device cannot always convert every particle. Soot can collect in it, clogging it over time. If soot fills the DOC’s pores or substrate, it can harden, impairing the device’s function.
DOCs typically incorporate coatings of rare metals (often platinum and palladium) known for their high catalytic properties. These elements accelerate the oxidation process, and they enable oxidation at a lower temperature than would otherwise be necessary.
However, substances found in certain diesel fuels, sulfur compounds, and oil additives can cause the metals to degrade. Ultra-high exhaust temperatures can also break down the rare metals, as the heat can sinter the metal particles.
While too-high temperatures can damage DOCs, too-low temps also cause problems. Though the DOC is meant to run continuously while the truck runs, it also has a “light off” temperature. When exhaust dips below that temperature threshold, it turns off, unable to oxidate the pollutants.
Exhaust temperatures can drop if:
The exhaust system lacks effective insulation against cold climates
The fuel injector timing is off, allowing too much cooling
There are leaks or excessive back pressure
The exhaust temperature sensor is dysfunctional or broken
Exhaust leaks are tears, holes, or gaps within the exhaust system parts that let exhaust waste and fumes escape the directed course, disrupting the flow of the system’s gasses. Depending on location, leaks can let hot exhaust gas and hydrocarbons bypass the DOC.
The unplanned outflow of hot gas lowers the temperature of the exhaust remaining in the system. As a result, the DOC may not be able to oxidate the exhaust, leading to dangerous levels of soot buildup.
Moreover, the change in pressure due to airflow shifts increases stress on the DOC. This, too, can exacerbate wear and deterioration.
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The different, interconnected systems of an engine are in an enclosed space. Misaligned, damaged, clogged, or otherwise poorly functioning parts along the whole exhaust chain often impact the DOC. The most common culprits are:
Turbochargers
Fuel injectors
Coolant system parts
ERG valves
To fix a damaged DOC, or to prevent it from getting bad, there are a few useful strategies to try. These include:
Regular monitoring
Cleaning
Component repair or replacement
Monitoring can be done at regular intervals using comprehensive digital systems. Drivers can also integrate an NO₂ monitor, as a sudden increase or drop in NO2 production can indicate a problem.
Cleaning the DOC is best done at an automotive servicer with a specialized thermal oven designed to bake soot off exhaust system parts.
That said, it’s also possible to use highly pressurized air to blast clean a DOC, or utilize precisely formulated liquid solvents. No matter which route you take, though, working with an automotive professional is the only way to safely clean these engine parts.
Upon inspection, a DOC may need to be repaired or replaced. A replacement requires compatibility with the exhaust system at hand, and necessary specifications are typically listed in the truck’s owner’s manual.
If your exhaust system is in trouble, don’t delay any longer. Instead, connect with the experts.
Our professional, certified technicians specialize in solving the particular problems faced by heavy-duty vehicle drivers. No matter what your diesel engine dilemma is, we've got it covered. For an appointment or consultation, call us at 1 (412) 264-.
This page provides regulations for nonroad compression-ignition (diesel) engines that are used in machines that perform a wide range of important jobs. These include excavators and other construction equipment, farm tractors and other agricultural equipment, forklifts, airport ground service equipment, and utility equipment such as generators, pumps, and compressors.
EPA has adopted multiple tiers of emission standards. Most recently, we adopted a comprehensive national program to reduce emissions from nonroad diesel engines by integrating engine and fuel controls as a system to gain the greatest emission reductions. To meet these Tier 4 emission standards, engine manufacturers will produce new engines with advanced emission control technologies. Because the emission control devices can be damaged by sulfur, we have also adopted requirements for in-use diesel fuel to decrease sulfur levels by more than 99 percent. The resulting Ultra Low Sulfur Diesel Fuel has a maximum sulfur concentration of 15 parts per million.
Data for reproducing real-world activity of various nonroad compression ignition (CI, diesel) engines in a controlled setting is available on this page:
EPA Nonregulatory Nonroad Duty Cycles
See the Electronic Code of Federal Regulations (e-CFR) for the full text of current regulations that apply to large CI engines.
e-CFR link Summary of what you will find 40 CFR Part Tier 4 emission standards and certification requirements 40 CFR Part Exhaust emission test procedures (for lab and in-field testing) 40 CFR Part General compliance provisionsBelow is a list of all regulations related to emissions from heavy equipment with compression-ignition (diesel) engines.
*Note: Rule-related materials vary by rule.
The company is the world’s best diesel emission parts supplier(fr,pt,es) supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.
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