Obscure control law: "D" vs "P" autostop

Many of us are aware of the 'Stage 4' shutdown when the engine finally stops when the Prius is not moving. This typically happens at a stop light or stop sign while the car is in "D". It also means the car will finally shutdown the engine at any speed from 0-42 mph. But I had noticed that when I got home and put the car in "P", the engine would suddenly start running until I turned it off.

I did some tests earlier this week and discovered that if I put the car in "P" when stopped, it would go into 'Stage 4' just like it would if in "D" and holding the brake. But unlike "D" mode, 'Stage 4', it would not suddenly start the engine if I shifted into "P" later.

It is a very obscure part of the control laws and has practically no useful effect. Still I wanted to share.

FYI, I also noticed that if the vehicle is stopped, I can shift into "N" and wait for the ICE rpm to fall below 1,000 rpm. Then wait 2-3 more seconds and shift into "D" or "P" to have it go into 'Stage 4.' Having the car in "N" inhibits attempts to charge the battery so the engine ECU will let the engine spin slower, under 1,000 rpm. A couple of seconds, 2-3, and shift and the car goes into 'State 4.'

Bob Wilson

ps. Nine years with this car and I finally figure this out!