150,000 mi 2007 Prius with a lot of dash error lights.

Help and welcome to Prius Chat.

I'd just like to remind you that you should start your own thread or if you are going to tag onto another make sure it is on the same subject. The hijacking of another poster's thread is to be avoided.

Umm, no. The MIL (message indicator light aka CEL (check engine light)) clearing was just coincidence. With the oil 1 qt low, there still would be 0.5 qt up on the dipstick. Technically, if the oil is between the L and F marks on the dipstick the oil is not low. Still, it was a good idea to add oil, but not your problem. Additionally, low oil does not set the MIL as there is no oil level sensor. When there is NO oil in the sump you will get the MIL and a symbol of an oil can on the MFD, which mean low engine oil pressure and means absolutely stop IMMEDIATELY and turn off the engine until you add more oil or you will permanently damage your ICE (internal combustion engine), if you haven't already.

The fact the MIL cleared on its own most likely means it isn't serious – yet!

This is very good advice, especially as Gen 2's get older. It also what Toyota advises doing regularly from the get-go.

If you do your own oil changes, you might want to consider using a product like Wynns Engine Clean (or equivalent) just before changing the oil. Consider also, using a good quality fully synthetic engine oil as well. If the problem is a stuck (or gummed up) oil ring, these 2 measures can free the oil ring and reduce oil consumption. Several people have had success with this. If you don't do your own oil changes ask your service provider to use it before draining the oil.

Back to your original problem, and in the future, always have the codes read when you have an error light come on so that you can get an idea of what might actually be wrong. With luck, it still might be there in the History column/section.

This can be as easy as pairing a Bluetooth dongle with Torque Pro ($6) android phone app. Ensure to read on the Torque Pro website for compatible BT dongles that work reliably with that app.

I hope that helps.