Everything You NEED to Know About P0420/P0430 Engine Codes!

[@MarzNet256]

I had an intermittent p0420 caused by a leaking exhaust donut made worse by worn engine mounts (code would mainly occur going up steep hills or hard pulls on highway). I used the torque pro app and a elm325 adapter to read DTC and graph voltages of upstream and downstream sensors. Upstream sensor was switching normally, while the downstream sensor was reading lean. A new donut gasket and all new engine mounts (OEM) fixed it. Car is a 2006 Toyota Matrix with 227k miles.

[@8020Media]

M - Thanks for taking the time to share your experience! This could certainly help future viewers.