Emission Technology Troubleshooting Diesel Oxidation Catalyst - DOC Typically, it is not the DOC that fails, but something that has gone wrong upstream. Excessive black smoke and low duty cycles will cause DOC face plugging. In such a case the DOC will have reduced performance and cold regeneration may occur. Eventually, the face will be plugged, creating restricted exhaust flow and excessive back pressure. Common DOC Failures The HC injector is clogged: Fuel can mix with soot to clog the injector. EGR coolant leaks & turbo fails: Oil and coolant sent downstream will contaminate the precious metal coating, leading to DOC inactivity. An inactive DOC will struggle to raise the temperature needed for a proper regeneration. The air filter is full: The DOC needs air when it ramps up to go through regeneration. If the air filter is full or clogged, the DOC will not receive enough air. When do you see failures in the DPF? Diesel Particulate Filters can fail due to upstream events or due to high mileage. Common DPF Failures Engine and Fuel system failures: Over-fueling injectors or a leaking aftertreatment injector will cause temperatures to raise too high resulting in the substrate melting or cracking. Oil entering the exhaust will also cause an uncontrolled thermal event. EGR cooler leaks & turbo fails: Oil and coolant sent downstream will contaminate the PGM coating. Air induction system failure: A restricted air intake system will cause excessive black smoke and result in frequent regens. Milege and replacement intervals: A DPF, like any other filter, has a limited-service span. It is advised to adhere to the cleaning interval specified by your engine manufacturer. For optimal performance, we recommend replacing the DPF with a reconditioned or new unit after reaching 125,000 miles for distribution vehicles and after every 250,000 miles for long distance vehicles. An alternative option is to clean the filter, which however is likely to reduce this service span. Visible soot from tail pipe The DPF may eventually crack due to excessive and unusual thermal conditions, allowing unfiltered exhaust to escape. Physical damage, excessive amount of trapped soot, or repetitive improper cleaning may lead to these cracks, and the filter should be replaced by a new unit as soon as possible. Selective Catalytic Reduction - SCR Typical SCR failures has their root causes in other system components that stop working properly, such as the Mechatronics controlling the system, or engine related failures. Common Failures causing problems with SCR Failures in DEF system: Leaking DEF injectors will cause DEF crystallization in the SCR. In addition, using DEF that is not the proper concentration or is contaminated will cause issues with the SCR. Failures upstream: Contaminants such as engine oil, coolant, or other impurities can damage the SCR catalyst, reducing its efficiency in converting NO into harmless gases. X Mechanical defects of substrate: Over temperature from an upstream issue will cause the substrate to crack or lose its ability to convert NO . X 7
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