Question

2007 Nissan Altima with code P0420, Cat efficiency below the threshold (bank 1). What does the code mean?

Answer 1

YOU NEED A NEW  CAT  

The catalytic converter stores oxygen. The efficiency of the TWC is determined by the measurement of the oxygen storage capacity (OSC). The engine control module (ECM) measures the catalyst OSC by monitoring the heated oxygen sensor (HO2S) bank 1 sensor 2 and HO2S bank 2 sensor 2, during a steady state cruise. The ECM commands the air-to-fuel ratio lean and then rich for a calibrated number of cycles while monitoring the response time of the HO2S 2. The ECM then establishes an average response time from subsequent air-to-fuel ratio cycles. The difference of the average response time determines the OSC of the catalyst. If the ECM detects low TWC efficiency DTC P0420 for bank 1 or DTC P0430 for bank 2 sets.