2010 Toyota Prius has bad fuel mileage?

It is extremely hard to get it that low with just driving habits. After all, stop and go is the sort of driving the Prius thrives in.

Historically, most cases of Toyota hybrid systems getting very bad fuel economy have come down to fuel injector problems. It was fairly common in the first generation, and usually under warranty, so the mechanics replaced the injectors. Instead, I would recommend adding a bottle of Techron to the gas tank and rechecking economy when the tank has burned off. The atkinson-miller engine in the Prius does much better on top tier gasoline brands and if the 46K miles (awfully low for 7 years!) were with random gasoline you can expect it to be congested.

The rest can be addressed by free inspections. As Andy says, have the parking brake checked as part of an overall brake check. If any of the brakes are visibly worn that explains the horrible mileage! Also have the 12V battery load tested, a free service wherever car batteries are sold. It may be nearly kaput. The Toyota hybrid system does not use the 12V battery for cranking so it is often a surprise when the lights are all dark one morning, and the DC-DC converter inside the inverter needs a good 12V battery to keep noise on the 12V system down. With a dying aux battery all sorts of odd things happen, including poor fuel economy.

Must be all stop and go driving. Do an OBD2 code check to see if there are malfunctions. Be sure about your mpg measurement before you tear into the car. As you watch the video read out, consider, instantaneous conditions do not equal average performance.

If the car is mechanically sound the problme is your driving habits.

First: make sure the tires are correctly inflated to the Toyota specified pressure, which might be over 40psi (unusually high for a small car, perhaps NOT 34psi). Second: make sure the parking brake and other brakes are not sticking on, causing drag and wasting fuel. Third: drive the car in D-mode, not B-mode, unless you actually need engine braking down a long hill; B-mode over-rides all the Prius hybrid energy saving and recovery systems, wasting fuel by keeping the engine running all the time. If all the car’s systems are working normally then you or your wife might be driving wrongly (jackrabbit starts, hard braking, etc); Car & Driver were able to get the Prius down to 18mpg by leadfoot driving on a racetrack.