Check Engine Light P0420 - Catalyst below threshold bank 1 - Toyota corolla 1999?

M D

My check engine light came on the 1st time, reason was the 02 sensors were burned out. Replaced them ($400 incl. labor). Then, 2 weeks later, check engine light came on. The reason this time: reading was a P0420, catalyst below threshold, bank 1. Mechanic suggested that I change oxygen sensors, perhaps the cables, too. I decided to wait. 2 days later, the check engine light turned off. Is there any rhyme or reason to this?

Silverstang

If you had already changed the O2 sensors, then there is no need to change them again. When it states that catalyst is below threshold, it usually means that the cat, is not working like it should. How many miles are on your ride? If allot, like well over 100,000, then maybe its due for another cat then.

GUS0921

WHEN YOU HAVE CODE P0420 ON YOUR VEHICLE MEMORY,IT IS NEVER RELATED TO THE 02 SENSORS.WHEN YOU GET THIS CODE IT IS ALMOST CERTAIN THAT YOUR CATALYTIC CONVERTER IS DETERIORATED AND NEEDS TO BE REPLACED.IN TEXAS U.S.A. IT COSTS AROUND $1000 TO REPLACE IT.GOOD LUCK.

GUS0921

WHEN YOU HAVE CODE P0420 ON YOUR VEHICLE MEMORY,IT IS NEVER RELATED TO THE 02 SENSORS.WHEN YOU GET THIS CODE IT IS ALMOST CERTAIN THAT YOUR CATALYTIC CONVERTER IS DETERIORATED AND NEEDS TO BE REPLACED.IN TEXAS U.S.A. IT COSTS AROUND $1000 TO REPLACE IT.GOOD LUCK.