We own a 2010 Prius II with about 40K miles; it's used almost exclusively by my spouse for stop and go commuting to work. I drive it occasionally, usually on the highway. The last two times I've driven it on highway(both in the past month), the engine, never very quiet anyway at highway speeds, would suddenly rev very, very loudly in the middle of the drive. This occurred on flat stretches of road, and I was just trying to maintain 65-70mph. I first noticed it when I attempted to engage the cruise control, which would not engage. And by suddenly, I mean that, on level ground at 65, with accelerator depressed to maintain speed on relatively level ground, the engine began revving much much louder than usual. No tach on car so can't give RPMs. I drive this car only occasionally and only occasionally on highway, but don't recall this being an issue in the past. My technical skills are very limited, and it's not my car, so any insights are appreciated. It's been a good car for us-bought new-and is only hybrid we've owned. No apparent issue with unusual revving in city stop and go driving. Thanks.
I wonder if you were in B instead of D? Cruise control will not engage in B, plus if you lift off the gas pedal, it will rev loudly...
I've noticed odd rev up, in the first few minutes after start-up, after the 12 volt battery had been disconnected. Like the car's doing some recalibration. In your case, not sure.
Strange combination of symptoms. Once the engine warms up a bit, it will run harder for a while as it puts charge back that it borrowed from the HV battery during warmup. But that won't keep the cruise from engaging and it really shouldn't be that drastic of a noise increase. As for B mode, I don't ever use it, but I seem to remember experimenting with it and could not go directly from P to B. Had to go to D first and then B, so if my memory is correct, it would be hard to got to B accidentally. But that would explain the cruise control and might explain the engine revving. If you are keeping a steady pressure on the throttle, though, the engine should run at a steady speed. Or very close to it even as it transitions from one warmup stage to another. I think I'd get professional help.
