About a month ago I got the dreaded P0420 (catalytic converter efficiency low) code on my 2005 Chrysler Pacifica. I did some diagnostics and found the downstream O2 sensor was ‘lazy’ (the voltage wasn’t changing with the upstream sensor). I replaced the downstream O2 sensor and now I get a P2097 code (post cat converter fuel mixture rich) and still the new O2 sensor isn’t changing voltage by more than .1 volts. Any suggestions what else it could be?
Replace the upstream O2 sensor. It’s much less expensive than a new cat.
Both sensors need to be on the same page, not 100K miles apart…
“the downstream O2 sensor was ‘lazy’ (the voltage wasn’t changing with the upstream sensor)”
The downstream O2 sensor is supposed to appear “lazy”.
The functioning cat converter acts as an O2 reservoir. Like a capacitor to those of us into electronics.
Your emissions system should still be under warranty. At least the cat would be.