One problem related to gas recirculation valve (egr valve) has been reported for the 2010 Toyota Prius. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2010 Toyota Prius based on all problems reported for the 2010 Prius.
Excessive oil consumption, particularly with highway driving. I have had this car for about a year. I only noticed that the oil was nearly empty when the engine was shaking while idling at an intersection. No warning lights for oil pressure or level ever came on, it would occasionally "ding" for oil pressure, but barley long enough for me to even read what the warning was. By excessive, I mean very excessive. First oil change after only 3k, almost empty. Road trip, mainly highway only about 600 miles, nearly empty. If I top it off, I check it constantly. City driving (more electric) it may burn a quart every 1-2k miles, highway more. I had the egr, manifold and plugs serviced/replaced, it improved slightly. I'm having more work done now, but after reading so many similar complaints online, I find it hard to believe this isn't a recall. An engine sputtering and nearly dying while idling is not safe, especially with no warning lights on! I contacted Toyota, they said they had not recalls or consumer confidence programs for complaints of oil consumption and/or piston ring seat problems in these vehicles (seems to be the primary cause). I did see a class action for many other Toyota 4cyl engines due to excess oil consumption.