miles per gallon dip

You do not mention how old your Prius is, but there are several 12v battery failures that result in reduced mileage. Is your 12v battery about 4 years old?

 

Judging from your previous posts, we really need more information. If the mods don't move this to the gen II fuel economy fourm, please start a new thread in the there and please answer the questions at http://priuschat.com/forums/gen-ii-...-answer-these-questions-esp-if-youre-new.html.

We don't know anything about your outside air temperatures, what you're comparing to (what were the temps before), how you're driving and things you might've checked or had done to your car.

The question about "computer module calclates when to switch from engine to motor malfunctioning" isn't the right question to ask if you understand how the power split device works. See Toyota Prius - Power Split Device. Please also see the Understand the Prius sections at Graham's Toyota Prius. Also look at the sticky thread in this forum: http://priuschat.com/forums/gen-ii-...sion/29352-introduction-prius-power-flow.html.

We're taking shots in the dark if you don't provide us more info.

 

Tire replacement with other than OEM tires also can cause changes in mpg, as will changes in road surface temperature, e.g. sunny vs. cloudy, summer vs. winter, etc.