Auto scan reads code P0420 - "Catalyst Efficiency Below Threshold, Bank 1. Is this an oxygen sensor? I’m told there are three in the exhaust. Can I further isolate this or should I take the car to the dealer?
The code is refering to the catalytic converter efficiency. Here is a link to some info on the code.
It is the rearward oxygen sensor that generated the signal that caused the CEL to come on and threw the P0420 code…Oxygen sensors have a design life of 100K miles. My Crown Vic threw this code at 160K miles. I replaced both the rear sensors (left and right bank), reset the light and it has remained off…
I suspect the DEALER will try to sell you both CATS, and all the oxygen sensors generating a repair bill approaching $3000…
The mileage on your car would be helpful
Thx for the good feedback. My car has 120k miles. To date I have replaced the bank 1 sensor and the MAP sensor.