P0421 AUDI – Warm Up Catalyst Efficiency Below Threshold Bank 1

P0421 AUDI Possible Symptoms

Engine Light ON (or Service Engine Soon Warning Light)

P0421 AUDI Possible Causes

Warm Up Three Way Catalytic converter deterioration or malfunction,Exhaust system leaks,Loose front or rear HO2Ss,Faulty front heater O2 sensor,O2 sensors harness is open or shorted,O2 sensors poor electrical connection

P0421 AUDI Description

The Engine Control Module (ECM) monitors the switching frequency ratio of heated oxygen sensors 1 (front O2 sensor) and heated oxygen sensors 2 (rear O2 sensor). A three way catalyst converter (Manifold) with high oxygen storage capacity will indicate a low switching frequency of heated oxygen sensor 2. As oxygen storage capacity decreases, the heated oxygen sensor 2 switching frequency will increase. When the frequency ratio of heated oxygen sensors 1 and 2 approaches a specified limit value, the three way catalyst malfunction is diagnosed.