P0423 Toyota Heated Catalyst Efficiency Below Threshold Bank 1

Possible causes

– Air leak before catalytic converter
– Faulty oxygen sensor
– Faulty Catalytic Converter

Tech description

As the code description implies the P0423 Toyota code means that the vehicle’s control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be replaced to fix the problem. If the P0423 Toyota code is combined with other codes, try fixing the other codes first.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P0423 Toyota 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.