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When do you see failures in the DOC? Typically, it is not the DOC that fails, but a failure happens upstream. This causes the DOC to stop working and you get cool regen. Common Upstream Failures The HC injector clogged. Fuel can mix with soot to clog the injector. EGR Coolant Leaks & Turbo Failures. Oil and coolant sent downstream will contaminate the PGM 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 regen. If the air filter is full or clogged, the DOC can’t get air. What is a DOC? DOC stands for Diesel Oxidation Catalyst. The DOC oxidizes carbon monoxide (CO) and hydrocarbons (HC) which creates an exothermic reaction that works in conjunction with the DPF by heating the exhaust going into the DPF. This ensures that the exhaust is hot enough to burn the soot into ash in the DPF. How Does a DOC Work? When an active or manual regen is required, the HC (hydrocarbon) injector adds a bit of fuel into the exhaust system. The HC injector is also called the fuel doser or after treatment injector. The dosed diesel goes onto the DOC, which, by catalytic reaction heats up the DPF. EGR Cooler Air In FM Filter DOC Turbo DEF tank Tailpipe DEF Injector DOC DPF SCR EPA 10 8
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What is a DPF? DPF stands for Diesel Particulate Filter. Its purpose is to filter Diesel Particulate Matter (PM), also known as soot, out of exhaust gasses. How Does a DPF Work? Trapped PM PM CO HCs PAHs SO 2 NO Types of Regen Passive: Automatic regen that occurs when the DPF reaches the correct exhaust temperatures. Plugged Cells CO 2 H 2 O SO 2 NO Exhaust gasses containing soot enter the DPF. The filter traps any matter larger than one micron, allowing gasses through. Over time, soot builds up in the DPF. Eventually, this causes backpressure detected by the Engine Control Unit (ECU) necessitating regeneration. Regeneration (regen) requires high exhaust temperatures of 1,058°-1,382°F. Combining high temperatures and a unique mix of precious metals washcoat the substrate turns soot into ash. The DPF is now regenerated and ready for use. Active: If a regen doesn’t complete a cycle, but sensors indicate DPF has reached capacity, an active regen occurs. The DPF dashboard light indicator will come on and the vehicle must continue to move to finish the cycle. Manual: If an active regen can’t complete, typically due to short drive times, then a manual regen will be required in a shop. EGR Cooler Air In FM Filter DPF Turbo DEF tank Tailpipe DEF Injector DOC DPF SCR EPA 10 9
