P0421 HYUNDAI – Warm Up Catalyst Efficiency Below Threshold Bank 1

P0421 HYUNDAI Possible Symptoms

Engine Light ON (or Service Engine Soon Warning Light)

P0421 HYUNDAI Possible Causes

Three way catalyst converter Bank 1,Exhaust tube,Intake air leaks,Fuel injectors may be faulty,Fuel injector leaks,Spark plugs may be faulty,Improper ignition timing,Engine Control Module (ECM)

P0421 HYUNDAI Description

The catalyst??? efficiency is demonstrated by its ability to oxidize CO and hydrocarbon emissions. The Powertrain Control Module (PCM) compares the output signals of the front and rear oxygen sensors to determine whether the output of the rear sensor is beginning to match the output of the front oxygen sensor. Air/fuel mixture compensation keeps the frequency of the front oxygen sensor high due to the changes from rich-to-lean comvustio. The catalyst causes the rear oxygen sensor to have a lower frequency. As the catalyst wears, the rear oxygen sensor??? signal trace begins to match the front oxygen sensor??? signal trace. That is because the catalyst becomes saturated with oxygen and cannot use the oxygen to convert hydrocarbon and CO into H??? and CO??with the same efficiency as when it was new. A completely worn catalyst shows a 100% match between the frequency of the front and rear sensors.