About 3-5 years ago she left her car with us while she was out travelling. It had the P0420 code. It's been that way since and after changing the downstream O2 sensor I cleared the code and it hasn't come back after taking a long drive.
Yeah that is a bit pushy. At least they say "or equal". Funny thing is, the bulk Toyota 0W20 I'm getting through dealership is cheap as dirt for me right now: $25.20 (CDN) for 9 liters ($2.80 CDN per liter). The operative word is "bulk", but I welcome that, I was getting tired of contributing to all the used motor oil bottles. They also sell it bottled, for around $6 (CDN) per liter, IIRC.
FWIW I've been buying Mobil1 and whatever other fully synthetic brand out there has a rebate. The last time I did it you could get a 5 qt jug and filter (~$35) and then get a $17 rebate and you could do 4 of these. That turns out to be $18 total. Figure the filter is $10 the qts of Mobil1 are $1.60. I bought four sets and have oil for a while. Just about every company has done this the past few years.
Well, since the manual says Toyota brand or equivalent and Mobil1 makes Toyota's synthetic oil, M1 is probably fine. LOL! I have used Toyota, Mobil1, and Pennzoil. Never a problem. And back in the day, Quaker State, Castrol, Rotella, and even Royal Purple. The last two were in motorcycles. On the transaxle, the oil changes are so infrequent that I'm not about to experiment with someone else's oil to save $5-$10 every five to ten years per car. Either way, good on ya for taking care of your own car. Most drivers don't know how to open the hood. And welcome to Prius Chat.
