How to Fix Code P0422: Causes and Solutions

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When you see the Check Engine Light illuminate and see the P0422 code, your first instinct may be to panic. Many things will enter your mind like, "What's wrong with my car?", "Am I going to have to spend a lot of money?" 

Don’t fret! As we know how to help you. This blog post will go over code P0422, its symptoms, and its causes. By the end of this article, you'll know how to fix code P0422. Read on!

What is Code P0422?

P0422 is a diagnostic trouble code for "Main Catalyst Efficiency Below Threshold (Bank 1). The catalyst or catalytic converter is designed to reduce harmful emissions from a vehicle. The Powertrain Control Module (PCM) monitors the catalyst efficiency using a post catalyst oxygen sensor. 

If the PCM detects that the oxygen sensor's signal is not switching as it should or if the capacity of the catalyst is likely to be less than the threshold, it will set the P0422 code.

Symptoms of Code P0422

The catalytic converter is one of the most significant components of a car. As mentioned above, this is the one that helps reduce harmful emissions. So, if this part is not working correctly, you may experience these symptoms.

  • Check Engine is On
  • Engine stalling
  • Loss of engine power.
  • Excessive exhaust smoke
  • Decrease in fuel economy

Causes of Code P0422

When you see excessive smoke in your car's exhaust pipe, you may think a faulty catalytic converter causes it. That is a possible cause, but we need to diagnose any issues from the start fully. It is essential to know all possible causes for this error code before replacing parts. What are these common causes?

  • Defective catalytic converter
  • Faulty oxygen sensor
  • Contaminated engine oil
  • Loose or damaged wires and connectors
  • Vacuum leaks in the intake system

How to Diagnose Error Code P0422?

Before you start diagnosing this trouble code, try to back-read all the causes above, as they will help you properly diagnose the issue. Also, hover your mouse down and check the common mistakes part of this blog to ensure you're doing the right process.

Then, once you've done that, it's time to get your hands dirty. Here are some steps on how to diagnose this code:

Check for Other Trouble Codes

Scanning for other error codes is essential in every troubleshooting process. This will help you determine other issues associated with the P0422 code. Plugin your OBD scanner into your car's diagnostic port and turn on the ignition but do not start the engine.

The Check Engine Light will now be illuminated, and you can proceed with scanning for any other codes that may have been triggered. Don't forget to write down all the codes and freeze frame data.

Perform Visual Inspection

Another essential step you shouldn't skip is a visual inspection. Check all the wires and hoses near the catalytic converter. Also, check for any leaks or damaged parts and repair/replace them if necessary.

Check for Contaminated Oil

If you notice that the oil is dirty or contaminated, this could be one of the causes of P0422. So how to check it?

  1. Park your vehicle on a level surface, and don't forget to set the parking brake.
  2. Remove the dipstick and thoroughly clean it with a paper towel or rag. Reinsert it fully back in place,                remove the dipstick again, hold it horizontally, and read the oil level on the dipstick.
  3. What's the oil level? Check your motor oil's consistency before removing the dipstick.
  4. If your dipstick has a white, milky discoloration, it indicates that there has been too much water in your          engine oil.
  5. In that case, you need to change the oil as soon as possible if this is the case.

If you made any repairs but still get the P0422 code, you might need to replace your catalytic converter. But before doing it, assess yourself first if you have the tools, knowledge, and time to do it yourself.

If not, take your car to a professional who will be able to replace the converter for you with little difficulty. But since you arrived at this blog post in the first place, let's get started!

How to Fix Code P0422?

Are you sure you are mechanically inclined? Kidding aside! Are your tools ready? Make sure you have the following: 

  • Socket wrench
  • Adjustable wrench
  • Screwdriver
  • Penetrating oil
  • Rags

Step-by-Step Guide to Replacing the Catalytic Converter

  1. Locate your catalytic converter
  2. Once located, spray the penetrating oil on all the bolts holding the converter in place.
  3. Allow the oil to sit for about five minutes before proceeding to the next step.
  4. Using the socket wrench, loosen each bolt until they are entirely removed.
  5. You may need to use the adjustable wrench to hold onto one side while unscrewing the other side.
  6. Once all the bolts are removed, carefully lift the converter out and place it on a protected surface.
  7. The installation is the reverse of removal. Make sure you tighten all the bolts to the manufacturer's                 specifications.
  8. Test drive your vehicle to ensure no more error codes are present.

Common Mistakes When Diagnosing the Code P0422

Mistakes are normal when dealing with any vehicle code. However, they are avoidable if you have the right tools and knowledge. So we recommend checking the part of this blog first before you start diagnosing. Here are the common mistakes you should avoid:

  • Not checking what the error code means
  • Not inspecting for contaminated oil
  • Not scanning for other trouble codes
  • Not checking the engine vacuum
  • Not checking for leaks
  • Assuming that the issue is the catalytic converter without verifying
  • Replacing the catalytic converter without checking the other parts thoroughly.

Code P0422 FAQs

1. Is the P0442 code serious?

Yes, P0422 is a serious code, and you should not ignore it because it will lead to emission test failure.

2. Can I drive having this error code?

No, it's not recommended to drive with a faulty catalytic converter as you will be polluting the environment due to excessive smoke and fumes.

3. How much does it cost to fix this code?

The catalytic converter replacement can cost you around $1000 to $4000. But, depending on the causes, the price may vary.

4. What can I do to prevent the catalytic converter from getting damaged?

You can use a fuel additive that can help clean the engine and prevent the build-up of carbon deposits. You should also avoid short trips as this will not allow the converter to reach its operating temperature.

5. If my car has a code P0422, does it need a new catalytic converter?

Not necessarily! There are many causes for this code, and not all of them require the replacement of the converter. The best way to find out is to have your car inspected by a qualified mechanic.


The code P0422 is a serious car issue, but you can fix it yourself with the right tools and information. If you are hesitant in doing so, please contact a professional mechanic to help you get your car up and running smoothly.

How did it go? Were you able to fix it yourself easily? Let us know in the comment section below. As always, thanks for reading!