EVAP
Captures fuel vapor from the tank, stores in charcoal canister, purges to intake. Loose fuel cap = most common P0455. Test with smoke.
Emissions are the single largest source of CEL codes. Knowing the systems makes them straightforward.
Most catalyst codes (P0420/P0430) aren't the cat — they're upstream sensors, fuel trim, or misfire history.
Captures fuel vapor from the tank, stores in charcoal canister, purges to intake. Loose fuel cap = most common P0455. Test with smoke.
EGR recirculates exhaust to lower combustion temp + NOx. Cat oxidizes HC/CO + reduces NOx. O2 sensors give the ECM feedback for fuel trim.
Yes — and it'll cause a CEL, which is an automatic fail in most OBD-II states.