Check engine light on - code P1121

I get it and appreciate it: everyone has a limited pool of money, but a lot of financial demands. We can only dream of winning the Lotto/Power Ball, or our long lost Nigerian relative coming through with the inheritance.

Given the scarcity of money, we must pick-and-choose. The only thing I can offer is price shop when you have to buy parts.
Amazon, Camelback Toyota (Phoenix, AZ), San Bernardino Toyota (CA), & North Hollywood Toyota (CA). Camelback will match other online Toyota prices, thus the inclusion of San Bernardino and North Hollywood, for you to comparison shop. Since you are an AZ resident, you will be charged AZ sales tax if parts are shipped or will-call pickup. These three online Toyota parts are my preferred stores to shop.
2007 Toyota Prius Parts - Camelback Toyota Parts - Genuine OEM Parts - Free Shipping
2007 Toyota Prius Parts - Toyota of San Bernardino Online Parts Store
2007 Toyota Prius Parts - Discounted Toyota and Scion Parts and Accessories

As for tires, I stick w/ Costco b/c I like them and it is an excellent value. There is always a promotion of $70 off a set of four tires (Michelin or Bridgestone) going on. The $15 per tire install fee includes: mounting, life of tire spin balancing (5years or until 2/32inch), life of tire rotation (5years or until 2/32inch), road hazard warranty (5years or 2/32inch), non-TPMS valve stem. Tire disposal is cheap: $1.75/tire, IIRC. Cars with TPMS I think are charged $2/valve for a rebuild; I think there is no forgoing the TPMS rebuild for cars w/ TPMS. Always price shop and compare, to see/hear for yourself.

Alignment? Does each of your vehicles have a lifetime alignment policy? I purchased one back in 2011, for $120 from Firestone Tire. I just drop-off the car once a year, for an alignment check-up. It always goes out of alignment, and they bring it back into specs. I pretty much broke even after the first alignment. According to them, curbs, potholes, debris, and speed bumps, can easily cause the alignment to go out of specs.

Air pressure? The driver door jamb sticker of 35/33 is too low. Many here go 40/38 to get better MPG and treadwear.

 

Okay. Thanks for taking time to provide good info. Just got $95. from tread wear warranty on the Continental Pro Contact ECO Plus tires that lasted only 22K and 30K miles. So that helps. I'm thinking those tires, nice ride, but can't handle AZ heat and Prius suspension.