is a bad catalytic converter on 2012 Equinox common
I would have to say that incorrect diagnoses of bad converters are far more common than actual bad converters.
Dealer mechanic stated it is the converter BUT IS BAD BECAUSE OF OIL CONSUMPTION
That’s possible, continuous oil burning can ruin a converter. What evidence does he have? Plenty of vehicles burn oil without ruining the convertor.
Yes, Oil burning will kill a converter. Agree with @old_mopar_guy that far more converters are replaced than actually NEED replacing. You spend a bunch to replace it and the check engine light pops right back on 2 weeks later.
All this is speculation considering you didn’t tell us if YOUR 'Nox is burning oil, how much oil, or how many miles are on the SUV.
It’s not unheard of for cats to fail. One of the cats failed on our 2013 Highlander at 81k miles, as diagnosed and repaired by the Toyota dealership. I’m not sure exactly what was wrong with the converter, but the check engine light hasn’t returned since they replaced it 40k miles ago.
I also had the converter fail on a 1998 Dodge truck at around 150k miles. It started rattling, the material inside had broken away from the converter body.
No, it’s not common.
But the cat is warranted for 8 years/80,000 miles.
Is it still warrantied if the can prove something else, like excessive oil burning, caused it?
The manufacturer has a choice.
Either fix the problem that kills the cats, or keep replacing the cats until the 8 year/80,000 warranty expires.
But after that, then it becomes an on-going warranty issue.