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The exhaust and emissions system carries combustion gases away from the engine and reduces the pollutants they contain to meet emission standards. On modern diesel trucks this includes after-treatment devices such as the diesel particulate filter (DPF), the oxidation catalyst, the EGR system, and SCR with diesel exhaust fluid (DEF), alongside the exhaust piping and silencer.
Exhaust gas leaves the cylinders and passes through the after-treatment system before exiting the tailpipe. The DPF traps soot in a honeycomb filter and burns it off in a process called regeneration, the EGR system recirculates some exhaust to lower combustion temperature and reduce NOx, and SCR uses DEF to break NOx down into nitrogen and water. Together they greatly reduce the harmful emissions a diesel engine would otherwise release.
The DPF clogs with soot and ash and needs regular regeneration and periodic cleaning, while sensors, the EGR valve, and piping can fail or corrode. Signs include warning lights, loss of power or fuel economy, increased smoke, and a blocked DPF. Because a faulty engine part such as an injector or EGR valve increases soot and clogs the DPF, problems are diagnosed and addressed early, and after-treatment serviced as the manufacturer specifies.
The correct part depends on the engine model and the emissions system fitted. Confirm the part against the vehicle and engine specification before fitting.
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What does the exhaust and emissions system do?
It carries combustion gases away from the engine and reduces their pollutants, using after-treatment devices such as the DPF, EGR, and SCR to meet emission standards.
What is DPF regeneration?
It is the process of burning off the soot trapped in the diesel particulate filter, either passively from normal heat or actively by raising exhaust temperature, turning soot into gas.
What does the DEF in an SCR system do?
Diesel exhaust fluid is used by the SCR system to break down nitrogen oxides (NOx) into harmless nitrogen and water vapour.
What causes a blocked DPF?
Excess soot, often from a fault such as a faulty injector or EGR valve, or from driving conditions that prevent regeneration. A blocked DPF should be addressed promptly to avoid engine problems.