2002 Prius 190,000 miles Friday I had an oil change & tire rotation done at the dealer. Afterwards there was a kind of soft "whirl/whistle" sound. At first, I thought it might just be due to the tire rotation & fresher tread (fairly new tires). But I noticed that it only occurred when I let up the gas (ie: during regenerative breaking). It did not happen if I accelerated or played with the pedal to just use the electric motor. The regerative breaking also felt firmer, it wasn't quite as firm and hard as breaking mode, maybe 20%-25% between normal and breaking mode I was going to return on Monday and have the dealer take a look. Yesterday all the lights came on, and I dropped the vehicle off at the dealer. I also checked the oil and noticed it was overfilled. I had a tech at the dealer check and they confirmed it was overfilled. (A couple of years ago the same dealership over-filled the oil and had to clean out the valves and such.) So my initital theory was that they over-filled the oil. This made it more difficult for the regenerative breaking to turn the engine/generator system. And that was why I was hearing that soft "whirr" sound when I was coasting/regerative breaking. So that was my expectation of the problem. Now the dealer is telling me the battery is bad and it will be $2,900. (I am not sure I really trust the competance of this dealer, they've shown great incompetance in the past, and I am considering getting a second opinion.) I am concerned that they over-filled the oil and have damaged the car and are trying to burden me with the cost by claiming the battery has died (leaked) We've had no signs of problems or issues with the battery to date. Not sure if there is usually an accompianment of symptoms before failure (ie: poor mileage, etc). But our mileage has been very typical, toward the high end of our normal in fact. Please advise.... UPDATE: Dealer says it's a P3009 code. According to this chat, it's common for battery but means it's a High Voltage Ground Fault and could be other issues. priuschat.com/forums/generation-1-prius-discussion/96825-dreaded-code-p3009.html I'm just wondering if the over-fill of the oil making the engine harder to turn for the regenerative breaking could have caused the P3009 fault. Luscious Garage had a post describing inverter/transmission failure also giving P3009 code. However, they also note a "whirrr from regenerative breaking" as a symptom. This is EXACTLY what I was hearing. Now my stupid dealership wants to charge me a second diagnosis charge. Argh.