Technical Description of OBD-II Trouble Code
The main catalyst efficiency is below the required threshold for Bank 1.
What does that signify?
This diagnostic trouble code (DTC) is a standard powertrain code that applies to vehicles equipped with OBD-II. Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
A vehicle’s catalytic converter, also known as a catalyst, helps improve tailpipe emissions by converting hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) into water vapor (H20), carbon dioxide (CO2), and nitrogen (N).
The powertrain control module (PCM) monitors the efficiency of the catalyst using a post-catalyst oxygen sensor. This sensor is primarily used for this purpose and should switch at a slower rate than the front oxygen sensors. If the PCM detects rapid switching of the post-catalyst O2 sensor, indicating no change between the inlet and outlet of the catalytic converter, it interprets this as a malfunctioning catalyst.
Bank 1 refers to the side of the engine that contains cylinder #1.
Symptoms
Symptoms of a P0422 DTC may include:
Causes
Possible causes of a P0422 code include:
Possible Solutions
Catalytic converters contain precious metals such as platinum, palladium, and rhodium. Cheaper catalytic converters use fewer precious metals. It is important to note that certain vehicle makes are very particular about catalytic converters and the PCM’s monitoring logic. Just because a parts supplier claims a catalytic converter will work does not guarantee its compatibility. The vehicle’s engineering was designed with a high-quality catalyst in mind, and it cannot be replaced with a low-cost alternative. Additionally, there are different types of catalysts, and some vehicle makes may only accept specific types. Toyotas and Subarus are particularly known for this. Subarus require CARB certified catalysts to prevent the check engine light from illuminating and will not tolerate aftermarket catalysts, regardless of their cost.
Therefore, if you continue to experience this code after replacing the catalyst with an aftermarket one, it is likely the cause of the issue. If you have this code and have not replaced the catalytic converter, there are two probable causes: the catalyst is faulty or the engine is operating outside the optimal air:fuel ratio. A tune-up or engine repair may resolve the issue, otherwise, the catalyst will need to be replaced.
