Got a 2015 dodge journey2.4L 4 cylinder, had been driving it around with this code on for a few months, just couldn’t get it checked out earlier. came to the conclusion I needed a new Catalytic converter so I got one and installed it myself. Have been driving around for about a month or 2 now and i keep getting the same P0420 code. I have a FiXD reader that gives me live data and the 2nd O2 sensor (Post cat) the reading isn’t steady. it fluctuates from like 0 to .7 volts.
just looking for any advice on how to fix this issue, i’ve cleared the code at least 7 times by now but something must still be wrong. any help would be appreciated
does your OBD2 reader display live data and Graphed data…
get in and look at the O2B1S1 voltage in graph mode…
bring the RPMS up to 2500 and hold the throttle pedal steady… even if the rpms drift slightly… do you have a nice clean waveform… take 10 seconds and slowly return to idle… do you still have a good waveform…
then look at the down stream oxygen sensor voltage O2B1S2 voltage… again at steady throttle 2500… do you have a flat line between 0.6 and 0.7 or a reduced waveform voltage compared to the upstream oxygen sensors…
reduced voltage waveform on the secondary indicates the cat is reducing emission… a really good cat will at 2500 steady throttle put out a flat voltage between 0.6 and 0.7 volts.
the P0420 is indicating the downstream sensor is Not seeing a reduction in emission…
the entire emission control system… from the gas tank to every sensor and component is designed to feed the cat with the exact exhaust gas flow so it can work properly to reduce emissions…
if your upstream oxygen sensors are going wild… you have to figure out what is causing it…
clogged injectors… misfiring… vacuum leaks… air intake leaks . exhaust leaks…