I took my 2006 Pruis into the dealership for a 30K tune-up. Until this time, I’ve had a consistent average of 48-50 miles per gallon. Since driving away fromt he tune-up, my average miles per gallon fell to 42-43. For the past 2 months I can’t get over 44 no matter what I try to adjust with my driving. I took the car back to be checked at the dealership with a result of no findings. They thought maybe the gas companies use of Ethanol might be a factor, but I took the car in on a half tank of gas. They did check my tire air pressure and it was fine. I did not have my tired rotated as part of the tune up because I had purchased new tires within 60 days and at that time the tires were rotated. About the only tip I have is that the computer read-out seems to have more of a delay than in the past. If I remove my foot from the gas pedal, it will take a second to respond instead of the usual immediate response I used to have. I am planning to check the actual gas mileage at the pump to give me more data. Any ideas?
Try resetting the computer. I don’t know exactly how that’s done, but it probably involves disconnecting the auxiliary battery or pulling a fuse for a minute.
Checking the actual mileage at the pump is the only way to accurately check it. Colder temperatures will drop your mileage.
They thought maybe the gas companies use of Ethanol might be a factor,
It may well be part of the problem. Winter mix fuels have less energy per unit. That means lower mileage, as does winter temperatures and less sun light. All these factors together will add up to the kind of difference you are observing.
Is this your first winter with your 2006 Pruis?
You’re saying this started roughly when you got new tires, right? Were the new tires identical to the old ones?
Colder temps = more gas engine run time = lower mileage.
Colder temps = lowered tire air pressure = lower mileage.