Check engine light came on and reader indicated Code P0420... O2 sensor catalyst system efficiency below threshold.

My truck, an '18 2.7L 2wd with 13.5k miles on the odometer has been a great vehicle. Luckily, it's under warranty, but I'm not instilled with a lot of confidence.
Goes to Ford dealer on Monday.

How odd is it for an O2 sensor to fail on a truck with only 13.5k on it? 😞

 

It’s not a o2 sensor it’s a bad cat, but that’s why you have a warranty.

 

Quite possibly... But how does a Cat fail after 13.5k miles?

I'm thinking something upline from the Cat must have failed.

 

Cats can fail just like any other part, the fact that it failed under base warranty it shows there was a problem when the part manufacturer made them...

 

Or, could it be, a part upstream from the Cat caused the Cat to fail as well?

 

I don’t know why you’re worried? The down stream o2 saw a problem that upstream didn’t. That’s why it set the dtc, if you a had a problem upstream of the cat, the upstream o2s would have caught it. Downstream only double checks what the upstreams found..

 

Appreciate the info. I will follow up after the dealer assessed the problem. Hopefully it's not a time consuming repair.

 

The Check engine light decided to turn off on way to dealer...weird. I've got the code print-out and its stored on board the computer. This is going to be interesting.

 

OK, looks like the Cat bank01 is bad. The part won't be available for 2 days. The CEL went out by itself as I drive to dealer... I'm suspicious. I can't figure this out.

The technician said to definitely replace it though. He stated that he's seen a few 2.7L with the same problem and replacing that Cat seems to fix the issue. He noted a minor, isolated misfire at one point on the computer, but said it did not pose a concern. I'll know more in a few days.

 

depending on when your truck was build that misfire could end up requiring all high pressure injectors needing replacement under a TSB...had it happen to my old truck before the TSB was even out. started off as an occasional fishbite misfire, but eventually got to the point that the whole damn truck shook under light acceleration