How to diagnose a P0420 code in a 2005 Toyota 4Runner

Question

When raising RPMs front O2 sensor fluctuating while the rear O2 sensor is stable. Outlet temp of cat ~100 degrees hotter than the inlet.

Answer 1

Hi there

The front O2 should change voltage rapidly, the rear O2 sensor should change slowly. The wave pattern is like a rolling wave on a lake VS the front which is choppy. If it's not changing voltage at all, then that usually indicates the catalytic isn't clearing the exhaust like it should. The voltage on the rear sensor is the result of O2 modules collecting on the sensor and generating up to one volt.