P0420...O2 sensors less than a year old.

[liv2bike]

So I got the blasted P0420. The CEL came on a few weeks ago. It threw a P0171 and a P0420 at the same time. Truck running fine. No odors or cat rattles that I could sense. Disconnected battery and reset it. Been driving it for a week or so with no issues. CEL back on. Must have gone thru another cycle. This time it only threw the P0420 code. Still running fine. O2 sensors were replaced about a year ago, maybe a year and a half ago at the most. So P0420 could be...

- air leak before rear HO2S (heated O2 sensor) Bank 1
-AF sensor error
- fuel syst fault
- faulty cat

Thinking I will clean the MAF first and reset again. Could be bad O2 sensors again but I replaced with OEM parts. Also could be cat or cats...but I hope not.

Any other ideas?

TIA.

 

[mikebontoft]

I just love that code so much I know what it means... catalyst efficiency below threshold.

your first 02 knows how the engine runs and cycles it between rich and lean for optimal catalyst efficiency. if there is a leak before the sensor it will catch it as a lean condition. if its after that sensor the cat could get too hot on the lean part of the cycle. that can kill a cat if it gets too hot.

is it the original cat? it could also just be worn out. it certainly does happen. you have already ruled out a faulty rear 02 which the computer uses as a comparison from the front 02 to determine efficiency.

This is of course assuming the rear 02 is not a faulty part... wouldn't surprise me if it was bad. I've seen far too many bad parts out of the box lately. even a seized AC compressor. a new one.

 

[imboredeveryday]

you need a cat its simple 420 and 430 codes are all cat codes

 

[fun_runner]

you need a cat its simple 420 and 430 codes are all cat codes

Yep, you'll need a cat. The ecm sees the o2's cycling like they supposed to and see that the cat isnt doin its job. The p0171 is often caused be a dirty mas air flow sensor. Clean the MAF and get a new cat and you'll be good to go.

 

[mikebontoft]

agreed.

 

[liv2bike]

Thanks fellas. bout what I figured. Plan to clean the MAF this weekend then move on to the cat issue. Thanks.