Ses

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

Is this an oxysen sensor or catalytic converter problem? Is it driver or passenger side?

Usually a cat.

Bank 1 is Cyl 1 side which would be driver side. Cat efficiency meaning: if the cat is working correctly, the O2 sensor behind the cat would have a low voltage all the time after warm up. The O2 sensor in front of the cat would be changing constantly between .1 an 1 volt, normal for that one. So what's happening is the O2 behind the cat is starting to change voltage and go over a certain point to set the code. Which generally means the cat isn't working like it should, OR, there is an electrical problem. Cat is probably bad.

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

Is this an oxysen sensor or catalytic converter problem? Is it driver or passenger side?
Swap the rear O2 sensors left to right and right to left. If the code follows the sensor then the sensor is bad. If the code stays on bank one then the cat is bad.

Bad catalytic converter... or at least its on it's way out.

Hi, New to the boards. I got a 2000 Camaro SS and I just took it to Autozone for the SES. Code is P0420 - Catalyst System Efficiency Below Threshold (Bank 1).

I only have 15,000 miles on the car. I bought an extended warranty (2 extra years making a total of 5) but my warranty ran out in April :(

The only thing I did was have the muffler shop put a Flowmaster muffler on just for sound (didnt need it), but that was over a month ago and then SES just came on now. Are the two related? My muffler shop says no.

What should I do, just reset it ?

I am in Michigan.

Thanks in advance for any help !

My light has been on for 3/4 of the time Ive owned the car. I got used to it. Same code. It happened when I did my cutout. I just reset with the HPP3

Major emissions components like cats have a federal warranty period of 8/80.

I went to Autozone and reset the code. It has not come back on today with about 10 miles of use.

I keep my fingers crossed.

Thanks for the help !

Major emissions components like cats have a federal warranty period of 8/80.


Yup, 8yrs/80k miles and I've read where aftermarket cats have a federally mandated warranty of 5yr /50k mi.

The hard part is ... you don't know if it is the O2 sensor or truely the CAT.

You have to pay for the "diagnostics" and if it is the CAT, GM will pick up the cost.

I think the problem is ... it is normally the O2 sensor (at least in my case with only 15k miles on), and then you are screwed.

Even if it is the CAT, the dealer can tell you it was an O2 so they don't have to pay.

The O2 sensors are not covered in the warranty.

Tricky business ....

if you know someone with a non-contact thermometer, you can tell if the cat is working. the temperature after the cat will be higher than the temp before the cat. if its not, its not catalyzing(working) anymore.

something similar with the dealer replacing both o2 sensors (some code o2 perheat) and a air pump divertor solinoid. what the fck with only 25000 mi. but any way, paid my deduct and the light is off ever since, very inportant in ny for your inspection!