I have a code P0420 in my '04 Civic Si. The catalytic converter needs to be replaced, but I would like to try to fool the downstream O2 sensor instead. As the cat degrades, the voltages starts to fluctuate and mirror that of the up stream sensor switching between rich and lean. Basically, the PCM is looking for a steady reading of about .45 volts. I was thinking of tapping into a 5 volt reference wire from the PCM, and then somehow dropping the voltage down to .45 volts. Then I would send this back to the PCM as the down stream O2 sensor input. What is the best way to go about this? Thanks!

 

Unless it is legal in Utah to modify your vehicle for the express purpose of violating emission controls to avoid replacing a failed catalytic converter, you are asking us to help you do something illegal, which is a direct violation of the Terms of Service you agreed to when you joined.