P0422 - MAIN CATALYST EFFICIENCY BELOW THRESHOLD (BANK 1)

The Three Way Catalyst (TWC) aims to improve tailpipe emissions by delivering oxygen to the exhaust gases. It also converts hydrocarbons, carbon monoxide, as well as nitrogen oxides. This converts it into water vapor, carbon dioxide, and nitrogen, respectively.

The Powertrain Control Module (PCM) ensures that the TWC is efficient enough. To do this, it uses an Oxygen Sensor (O2) which is located on the back of the Catalytic Converter (TWC). The O2 sensor has a single purpose, it must change more slowly than the front Oxygen (O2) sensors.

If the PCM detects that the post-catalyst O2 is performing the changeover too quickly, it is interpreted as a malfunction of the TWC. Therefore, the DTC code P0422 is set.

• MIL light illuminated.
• Fuel consumption decreases.
• Increase in the exhaust emissions.

The factors that lead to the configuration of the error code P0422 OBDII are

• The TWC may be defective.
• The engine thermostat may be in bad shape.
• Oxygen sensor or its cables with defects.

When troubleshooting the diagnostic code P0422 OBD2, please note the following:

• Determine if the Three Way Catalyst (TWC) is working properly. To do this, run the engine at 2500 RPM for three minutes. Then, measure the temperature at the inlet and outlet of the Catalytic Converter. The output should be 200°F less hot than the inlet. If there is no such difference or no difference the TWC may be defective.
• If there is a noticeable difference, the Oxygen Sensor is most likely defective. That's why you should change it.