When selecting drive Prius will only go into neutral.

is it making ready the first time?

 

Anytime the 12v is reset it will take two (2) power cycles to "ready" the vehicle.

How are you currently starting the vehicle? (foot on the brake pedal, etc.)

 

Try pressing down on the brake, and hitting the power button twice. This is assuming your single power button push isn't long enough.

If there was a HV ground fault (leak) a DTC would be thrown.

Sounds like the advice given (inverter or leak) was in relation to DTC P0AA6, which you don't have.

 

yeah, that's getting down there

 

Make sure you always put your foot on the brake first, before hitting the power button, not just before trying to put it into Drive.

The car also needs to be "READY" before it can go into Drive. When Drive fails, is the "READY" status light on?

 

Pretty sure the power button isn't being depressed long enough, which is why I suggested pressing the button twice instead of once.

 

after I put my foot on the brake, I press the start button until I hear the first beep

 

It sounds to me like the OP is putting it into ACC, then puts his foot on the brake and hits the Power button again which makes it READY. Then it goes into D. But not sure if you can put it in N in ACC, but if he has actually hit the Power button twice with foot off the brake, he will be in IG-ON and it is possible the put it into N, but not D (obviously). Again from here if he puts his foot on the brake and hits the Power button again it makes the car READY and then it will go into D.

The table below describes the various Power states of the Gen 2 Prius:

	To get to this state ...	Do this ...	then this ...	Notes
1	ACC	Foot off the brake	press start button once.
2	IG-ON	Foot off the brake	press start button twice.	(Once again if in ACC)
3	OFF	Foot off the brake	press start button a third time.	(Once again if in IG-ON or READY).
4
5	READY	Foot on the brake	press start button once.

NOTES:

• Pressing the Start button once, with your foot ON the brake, from any of the above states (ACC, IG-ON, OFF), will start the car and make it READY to drive.
• When in READY and you press Power once (with your on OR off the brake), it will turn the car OFF.

 

I believe these two statements are the keys. I've had the same thing happen in a couple Prii.

When you press the Start button, it energizes relays that take time to latch. Give it a half second push rather than a quick jab. The situation is worse with a weak 12V because the relays move slower thanks to a weaker magnetic field in the coil.