One problem related to gas recirculation valve (egr valve) has been reported for the 2008 Toyota Prius. The most recently reported issues are listed below.
Our 2008 Prius experienced engine failure while driving CA. 70 mph on a day when the temperature was between 90 and 95 degrees. This appears to be the same problem with the inverter that has happened on later models, especially as �high thermal stress� featured in reports of those. Two mechanics were unable to pull a computer code on it and said they couldn't offer an opinion unless it was replicated. Each mentioned the inverter problem, but claimed that it could only have happened on model years more recent than ours. A Toyota company rep claimed never to have heard of it happening on any car before 2010. I asked if there were a database of such issues she could check to see if other owners had anything similar happen before 2010, but she declined to do so. I believe she claimed that the company maintained no such database. All I remember for sure is that she projected no inclination to follow up, appearing to treat it as a one-off problem that didn't merit further attention. This happened while I was passing a truck, with a car close behind clearly intending to pass me after I had gotten around the truck. I suddenly realized that I had no acceleration and that the dash lights had come on. I was luckily able to steer across the driving lane to the right shoulder without being hit as my speed dropped. I tried starting the car again; it started up as if nothing had happened so we continued, carefully, on our way. That specific problem has not reoccurred, although there were two incidents (one earlier that day and one the day before) when pushing �start� failed to start the engine. Dash lights and air conditioner fan came on, but engine did not start until the �start� button had been pushed twice more. In both of these cases the temperature was also in the 90s.