Full Battery & going downhill - Engine coming on?

My guess would be that it's kicking in engine braking like "B" does on my Gen-2.

 

Engine is on without burning fuel. Watch the display to see that no fuel is being used, then it's engine braking for sure.

 

does it go through the whole warm up cycle?

 

a minute isn't full warm up, even in warm weather, so that's good.

 

try ev auto and see what happens.

 

How is the engine on without burning fuel?

 

I go down a large hill everyday and the battery gets full. It's normal. The battery doesn't want to overcharge and therefore doesn't want to use the regenerative brakes. When I stop at the bottom of the hill, the engine revs pretty high. There are probably better ways this could be done because I'm always thinking in my head "I'm wasting gas going downhill! There's no more room in the battery!"

 

The HSD spins the engine without injecting fuel. You have to be moving, of course, and above a minimum speed for this to happen. You can see you aren't burning fuel by mileage displayed, and if you have a "Scangauge" you can see the fuel being used "instantly" (with about a 1 sec. delay). The "normal" Prius does this to keep control when descending a hill with the battery "full", and you applying the brakes gently. "Full" meaning it doesn't want to charge the battery any further. Computers understand differently than we do.

 

I had this happen yesterday, went down a hill and at the bottom the engine came on and it stayed on through the likely normal warmup cycle. It didn't go back to EV mode for 5 minutes. I did not have a full charge at the top of the hill, I was below 20 Mile range, but while the engine was on I started gaining range. It was almost like it was on charge mode. This same hill in the other direction causes the engine to come on going up so I am just going to consider this the Prime Curse Hill .

 

yes, that was definitely the warm up cycle. o/p's description of one minute, and average mpg's going down might be something new toyota has come up with, or just an error.

for anyone leaving there home and going downhill that fires the engine on a regular basis, the only solution on the pip was not to fill up the battery all the way when charging.

 

You connect the engine to the wheels......and then don't feed it any (or just a tiny bit) gas.
That is the definition of engine braking.

 

it's hard to remember if it's not something you're not concentrating on at the time.

 

Oh, I never knew that the HSD could power the engine at such high RPMs, interesting. Why doesn't the regenerative braking stop "regenerating" when you take your foot off the gas and the battery is "full?"

 

It does - it's using the engine's pumping losses to dissipate energy (turns the kinetic energy of the car into heat in the air).

 

On my gen 2, the green arrows are going from the wheels to the electric motor to the battery when the battery is full, so I thought it was trying to charge the battery still. I just learned a lot about a car I've had for almost 12 years. thanks!

 

That's normal behavior. Once you've used the motor-generator to fully charge the battery the extra regen energy has to go somewhere so Toyota kills the motor-generator by making the engine take the role.