I bought a 2011 QX56 in October 2020. Cat code came on in December, SES started blinking and limp mode in January, had to get it towed. Mechanic noticed the oil was low and dirty, implying it hadn't been changed for a while. I checked and the last time it was changed before I bought it was February of 2020. However, it only had 3,000 miles on it since the oil was changed. It was taken into the dealership for maintenance in July of 2020 but they didn't do anything to the oil, as I'm assuming they checked it and it was fine, especially since it was synthetic and very low miles since the last change.
So my mechanic changed the oil, cleaned out a sensor or two, told me to change it again in 500 miles (which I did) and gave it back. It drove great. For about a month. Then the SES light came on again (not blinking), took it to the mechanic, he changed the VVT solenoid. A couple weeks later, SES light was blinking, went into limp mode, had to get it towed again.
He cleared the code history, didn't do anything to it, said the oil did look a little dirty, recommended that I change the oil again and take it to the dealer next time the SES light came on which he figured it would, soon.
So I got the oil changed, drove it around for a while, about 200 miles away and back, twice. The light never came on, it never rough idled, nothing. For 3,000 miles. I changed the oil again two weeks ago, it runs great.
All that to say, I'm confident it was the result of not having the oil changed frequently enough in 2000, despite the low mileage. So I'm planning on getting it changed every 4 months. With full synthetic I was hoping to get away with less frequent changes, but apparently not.
______________________________