If your check engine light is on because of a P0420 or P0430 fault code (catalytic converter below efficiency) but you don’t want to shell out the dough for a new catalytic converter, you’ve come to the right place. This fix can also work if you’ve taken the liberty to remove your catalytic converter.


What causes a P0420/P0430 fault code?

The P0420/P0430 fault code is caused by the O2 sensor after your catalytic converter detecting that the emissions still remaining in your vehicle’s exhaust are above acceptable levels. Once it detects your catalytic converter is operating at 95% or less, it will determine your catalytic converter needs repaired or replaced. Your catalytic converter filters these emissions, typically using precious metals, hence why they are so expensive to replace.


What causes a catalytic converter to go bad?

A plethora of things can cause a catalytic converter to wear down over time. On older vehicles the metal make-up of your converter can corrode over time. Excessive heat can also damage your catalytic converter, this is most often caused by engine misfires. When an engine misfires, unburnt fuel makes its way into your exhaust system, and often one of the first things it comes in contact with is your catalytic converter. This fuel can then ignite in your exhaust system, damaging the catalytic converter. So, if you’re catalytic converter has gone bad a relatively newer vehicle, make sure your catalytic converter going bad isn’t a symptom of a different problem.


Make sure the check engine light is on for the P0420 or P0430, and not something else.

The easiest way to do this is attach and OBD II scanner to your vehicle and read the codes, if your only code is P0420 or P0430, you’re in business. If you have other codes as well as one of these, you can fix one of the codes, but the check engine light won’t go away until all the logged faults are taken care of.


What’s the difference between P0420 and P0430?

The P0420 and P0430 fault codes are the same code coming from different banks. P0420 is the fault code for bank 1, while P0430 is for bank 2. It is important to identify which bank the fault code is coming from. Where the fault is coming from will determine where we put our fix.


Will this fix my catalytic converter?

The short answer is “no”. This fix will not increase your catalytic converter’s efficiency. It will, however, remove the check engine light and potentially increase your vehicle’s performance. The performance increase will come from your vehicle no longer putting itself in “limp mode”. This occurs when your vehicle slows itself down so the catalytic converter doesn’t have to work as hard, and can filter as much of the emissions as possible. By keeping your vehicle from knowing the catalytic converter isn’t operating at 100%, it won’t slow your engine down. Keep in mind this “limp mode” is more likely to occur on newer vehicles.


What will I need to get rid of the check engine light?

You will need a drill, vice, half inch drill bit, and a couple 18mm spark plug non-foulers. You can pick up spark plug non-foulers at your local auto part store for less than $10. They are usually sold in either 14mm or 18mm, you will want 18mm for the majority of vehicles. These are made of aluminum, so they are able to be drilled through, given a little persistence.


What do I do with the non-foulers?

Simply drill all the way through one on the non-foulers, leaving the second one fully intact. This can be done play placing one of the non-foulers in a vice. Do not tighten down the vice too much, you will bend the aluminum much easier than you might think. You may want to wear gloves while you do this, not only to broken your hands from metal shavings, but because the non-fouler will be extremely hot after drilling.


Locate your oxygen sensor.

Once you have it drilled out, take your drilled out non-fouler and screw it into the one you did not drill out. Now you are ready to locate your correct oxygen sensor. To determine which oxygen sensor is the correct one, first reference your fault code. As mentioned above, whether the code is P0420 or P0430 will tell you whether the fault code is coming from bank one or bank two, respectively. Locate your catalytic converter of the bank your fault code is coming from. If in doubt which bank is which, you can always apply this fix to both banks, simply repeat the process. Once you’ve found the catalytic converter, there should be two oxygen sensors near it, one before the catalytic converter (where the exhaust from your engine enters the converter) and one after (where it exits the converter). The oxygen sensor you are looking for is the one after  the catalytic converter, this will not work on the sensor before the catalytic converter. Keep in mind these parts of your vehicle may be extremely hot and it might be a good idea to let your car cool down for a while before beginning to work on it.


Remove your oxygen sensor.

Once you’ve located the correct oxygen sensor, go ahead and remove it. In my own experience the oxygen sensors tend to come out easy enough with a wrench, but I have heard that it often takes some finagling to get them out. Now is a good time to clean it off if it needs it or check it for any damage, as that may be causing false readings. Now simply screw the oxygen sensor into your non-fouler (the drilling you did should have created just enough space to insert the sensor) and screw the non-foulers into where you just removed the oxygen sensor. There is no need to over-tighten the non-foulers, as you are likely to strip or round the aluminum. Just make sure it is snug.


How does this help correct the check engine light?

By creating space and limiting the air flow between your exhaust and your oxygen sensor, it keeps the sensor from being tripped. This is because the sensor is constantly sending voltage readings to your vehicle’s PCU, and when it reads exceptionally high or low spikes in these voltages, it tells your PCU something is wrong and trips the check engine light.  By creating a cushion for your oxygen sensor, it does not experience these sharp changes in voltage, and no fault code is logged, resulting in no check engine light.


Did it work?

To find out if the fix was successful, use your OBD II tool to remove the current P0420/P0430 fault code. Then go for a short drive and make sure your engine gets up to normal operating temperature. Keep in mind this fix does not work every time, and in no way fixes your catalytic converter, it is only meant to keep the check engine light from appearing. If the check engine light is still present or comes back, refer to your OBD II scanner to see if it is the P0420 or P0430 fault code. If it is, you can always try adding an additional (third) non-fouler, or putting a small amount of steel wool inside the current non-foulers, in an attempt to increase the cushion you’ve created. If the check engine does not return, the fix was successful.


Is this legal?

It depends where you live. If you live in an area or city where you vehicle must pass emissions tests, I highly recommend against doing this. If you aren’t certain what your local laws are on emissions and catalytic converter tampering, always err on the side of caution. As previously stated, this does not fix the catalytic converter itself, it simply fools your oxygen sensor into thinking the catalytic converter is operating normally.


Should I replace my catalytic converter?

At some point down the road, yes. This fix can be seen as a bandaid, not a permanent solution. It will get rid of the check engine light and fool your vehicle into thinking it is operating normally, but your catalytic converter is still not operating as it should. Which won’t adversely affect your vehicle itself, but means it is producing more harmful emissions than it should. With any fix like this, you will also want to be sure the catalytic converter going bad isn’t the side effect of a larger problem, such as a misfiring engine.


Hopefully you found this information useful and I wish you all the best of luck!