DTC P0420 – How To Install a Check Engine Light Eliminator

DTC P0420 – How To Install a Check Engine Light Eliminator


The DTC trouble code P0420 is for your Catalytic Converter either failing or malfunctioning to the point that your secondary 02 sensor is providing the ECU / PCM with a signal that exceeds the manufacturers guidelines. Today we’ll be walking you through How To Install a Check Engine Light Eliminator.

Other check engine codes may include P0134 : 02 Sensor Circuit No Activity Detected (Bank I Sensor 1)


This usually means that your catalytic converter or catalyst is in the early stages of failure, or more often than not you own a turbocharged vehicle and have removed the catalytic converter. Removing the catalytic converter may be a popular mod, but it’s also an illegal one if you intend your vehicle to drive on any public roads.

For more information check out our FAQ on how to determine your state’s emissions laws.


Today we’ll be showing you how to resolve this DTC OBDII trouble code in a 2006 Mitsubishi Evolution, however this code can affect almost anyone with a turbocharged vehicle from 1995 and above.

This code in particular refers to the secondary downstream 02 sensor, or the oxygen sensor located behind your catalytic converter. This secondary 02 sensor ensures that the catalyst is doing it’s job and the proper amount of oxygen is in the exhaust gases.

When your secondary 02 sensor sees values that are outside of your manufacturer’s designated values, this check engine code will go on. This signifies that your catalyst converter is faulty or the honeycombs and elements inside the catalyst have broken down or become damaged.

This will lead to your P0420 OBDII check engine code, which will cause your vehicle to fail any emissions tests specific to your state.

To resolve this issue, we’ll be installing a Weapon R check engine light eliminator, part number 963-111-102.

It’s time to see How To Install a Check Engine Light Eliminator, so let’s get started.


Installation of this unit is easy and very straightforward, and we prefer the brand Weapon R as we’ve been authorized dealers for over 20 years now. This Check Engine Light Eliminator has undergone quite a few changes, and we prefer the stainless J shaped unit it’s become now.

The 90 degree bend allows for installation with your secondary 02 sensor pointed upstream, or against the flow of exhaust gases. The stainless steel construction ensures many years of high quality, high finish, quality looks and fitment.

To begin locate your secondary 02 sensor, which should be installed downstream of your primary catalytic converter. In our Project Evolution equipped with HKS exhaust components, the secondary 02 is located directly behind the downpipe / testpipe.


As with all of our writeups and how-tos, Pro Street Online does not accept any responsibility for the work you perform on your vehicle. Use the utmost care and work with safety in mind first and foremost, and as always, if you are not comfortable working on your own car, please take it to an ASE certified mechanic.

Also understand that this modification may be illegal in many states, and is intended for off-road use only or in other words never for use on any public road. Please be responsible and research the rules for your state accordingly.


After you have your secondary 02 sensor removed, now undo the 3 14mm bolts that secure the 3 bolt testpipe to the 3 inch catback. Set the bolts and nuts to the side along with your 3 bolt 3 inch exhaust gasket. Let the catback hang down so that you have enough space to screw on the Check engine light eliminator.


Pull down the secondary 02 sensor and twist it counterclockwise so that when you screw it into your Weapon R check engine light eliminator you do not kink or damage the wires.


Now tighten the locking nut once you have enough of your check engine light eliminator screwed in ( can also be called de-fouler ) Notice the orientation of our eliminator, and how the opening for the secondary 02 sensor is pointed upstream, or against the flow of exhaust gases.

Reconnect the downpipe and catback, and you should now be ready to reset your ECU and enjoy a blank slate on your Evolution cluster!

You have now completed our How To Install a Check Engine Light Eliminator Guide. Congratulations.

Happy boosting!