Emissions & Aftertreatment

High pressure vs low pressure EGR: where each loop takes its gas, why modern diesels combine both, cooler and soot trade-offs, and what the ECU balances between the two.

GPF OPF particulate filters on petrol engines: why direct injection needs them, how regeneration differs from a diesel DPF and what pressure sensors report to the ECU.

The three DPF regeneration types — passive, active and forced — how the soot model triggers them, and why interrupted regenerations fill the filter and trigger limp mode.

Basic overview of EVAP logic, purge strategies and tuning implications for gasoline vehicles.

How ECUs react to clogged DPF filters, regeneration failures, and excessive backpressure.

Big picture view of how DPF, EGR, SCR, and catalyst systems cooperate for emissions compliance.

Secondary air injection pumps fresh air into the exhaust during cold start to accelerate catalyst light-off and reduce HC/CO emissions.

Extra fueling, timing strategies, and lambda management during cold start for catalyst light-off.

Catalytic converters reduce harmful exhaust emissions through chemical reactions. The ECU monitors catalyst temperature and efficiency using oxygen sensors.

Selective Catalytic Reduction (SCR) uses AdBlue injection to convert NOx into nitrogen and water. Essential for Euro 6 diesel compliance.

The Diesel Particulate Filter (DPF) captures soot from exhaust gas. The ECU manages soot accumulation, regeneration cycles and differential pressure monitoring.

Exhaust Gas Recirculation (EGR) reduces NOx emissions by diluting intake charge with inert exhaust gas. The ECU controls EGR flow based on operating conditions.