1998 Toyota Corolla Q&A
1998 Toyota Corolla Question: p0420
That is a catalyst inefficiency code. You need to have a good diagnostic test done to find out why. You could have a problem with the heated oxygen sensor, or the catalytic converter itself could just be not doing its job. If that's the case, you could have something else that has caused it to fail...so looking at it with a good diagnosis is in order. - DaveJHM
P0420 is low catalytic converter efficiency and may require a new cat converter to repair. Sometimes a failing O2 sensor can cause the code. If it is a failed cat converter make sure what caused the failure is addressed. - patrick mannion
Had the same problem. Change the catalytic converter, and see if that does the trick. If that is not the problem, It's the O2 sensors. - Visitor
...technician of TOYOTA SERVICES and they told that my car appears the Diagnostic Trouble Code "P0420" Catalyst System Efficiency Below Threshold (Bank 1) and they reset the alarm and they told me...
engine light on code p0420
Can a P0420 Error Code show up when a ECM is defective? What the code points toward is the Cata...
how to check to make sure cat. converter is bad
change everything plugs air fliter oil change front and back o2 sencers drove from god nos were its sayin on my freind machice it passes but engine light still on and i no i got to get it inspected...