P0420 Toyota -4 runner 1998

Question

My 1998 4 runner $ cylinder 2.7 L, failed emission test. Check engine light was ON
The engine code is P0420, Catalytic system efficiency below threshold (Bank 1).
I replaced the catalytic converter 4 years ago when it was stolen. The catalytic converter was bought from internet. I believe the cost was around 80 dollars.
There are many possible causes. One of the causes is the catalytic converter bank 1 oxygen storage is low.
Could the catalytic converter failed after 4 years ?
The exhaust tail pipe is very clean. No carbon deposit at all. At least 50% of the tail pipe ID surface shows original metalic clean that indicate the car is running lean. I am sure this car would pass the real emission test if the exhaust is checked.
Any suggestion what's the cause ?
Thanks

Answer 1

Hi there,

It is possible the converter is the problem. The O2 sensor doesn't store O2, it reads the amount of O2 coming out of the converter in the exhaust flow. If the rear O2 is faulty then it can cause the 420 code, but more then likely the converter is the issue.