Approx. 35 MPG instead of upper 40s now - 2008

I've got a twenty-oh-eight Prius with the package that includes GPS and 6 CD slots but not the leather seats. (I believe it was called option 5.) February 23 marks the 5th anniversary of the day I brought it home. I have just under 40,000 miles on it because I usually take the train to work (but do need to drive about a mile each way to the train station).

Last year, I had to replace the original tires. I ended up getting a brand I had never heard of before called Yokohama. No, I didn't get it at the Toyota dealer but at a local tire dealer. Another person I know who has a twenty-oh-eight Prius and got it two days later (with fewer options - option 1, I think) decided to do his Pennsylvania state inspection at the same tire dealer instead of at the Toyota dealer. This was in December twenty-twelve. At that time, he needed to replace his original tires, too. He has even fewer miles on his car because he works near home, and unlike me, he hasn't taken it on many out-of-town trips. The tire dealer tried to sell him Yokohama, too, but mentioned that it would make his MPG worse. My friend ended up getting Yokohama, but he got what the tire dealer said was a more upscale model that wouldn't degrade his MPG.

My MPG has suddenly drastically fallen to the mid-30s - 35-36 MPG. It was usually worse in the winter anyway, but the fall was from about 49 to about 45 or 46.

I had the car at the Toyota dealer for PA state inspection and the 40,000 mile checkup on Jan. 12. I asked them about the drop in MPG, but they said there was nothing they could do - it all had to do with the "computer" in the car. They also said they didn't think it was the tires.

Well, if it's the computer, then how do I get it reprogrammed?

Or is it the tires, and should I spend several hundred dollars on new ones, to improve the MPG?

Or is this beyond repair, and I should start thinking about getting a new Prius? (Shuddering at the thought of no trade-in value, and not being able to sell it for much myself due to the lack of the major selling point of a Prius.)

I know I'm a beggar who shouldn't be a chooser, but in years of using online help resources, I've found that the most useful responses I've received are typed in mixed case with reasonably good grammar and spelling, have most words spelled out, and do not contain emoticons.

Thanks (NOT thx or tks or ty) in advance (not TIA) for any help you (NOT u) can give me on this.

 

What questions?

 

Thanks for the quick reply.

Later this week, I'll carefully read through the instructions you've linked me to. After my quick perusal just now, I know I will have questions on where to get some of the tools that are mentioned.

I'll get my tire pressure checked this week, too.

 

I figured out that there was a link after I posted my reply and then saw the other reply that had appeared in the meantime had a line that was cryptic but turned out to be a link. The Super Bowl wore me out, so I will need to look at it later this week. (I'm not too thrilled to see one of those goshdarnawful emoticons in that message, however.)