2 weeks ago I replaced the bank 1 o2 sensors on my 1998 Honda civic and it took of my check engine light and then while driving and downshifting the check engine lights comes up again p0420 but says subsystem when I checked what does that mean! Look at my pics, the 2nd one is the one I have at the moment and the 1st one is the one I used to have before I changed the o2 sensors.
The code is telling you that the catalytic converter is no longer doing its job.
Thank you so now I just replace it then?
And here’s where you start.
Fixed the problem I replaced my whole catalytic converter with the intake manifold and the check engine light went away thank you