DTC P0420 & DTC P0430 Lexus ES XV30

Code Definition

1. DTC P0420: Catalyst System Efficiency Below Threshold (Bank No. 1)
2. DTC P0430: Catalyst System Efficiency Below Threshold (Bank No. 2)

Note. Bank 1 is also known as right bank (RH). Air/Fuel (A/F) sensor refers to sensor closest to engine block. Heated oxygen sensor No. 2 refers to sensor furthest away from engine block.

Circuit Description

ECM compares waveform of Air/Fuel (A/F) sensor located before catalytic converter with waveform of heated oxygen sensor No. 2 located after converter to determine if converter performance has deteriorated. If both waveforms change at similar rate, catalyst performance has deteriorated. DTC is set when A/F sensor and heated oxygen sensor No. 2 waveforms have same amplitude after vehicle is driven for 5 minutes at 20-50 MPH. Possible causes are

1. Leak in exhaust system.
2. Faulty A/F sensor.
3. Faulty heated oxygen sensor No. 2.
4. Faulty catalytic converter.

Diagnostic Aids

Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected.