Had to have it towed.

Kept having the "p=lock error" appear on my screen and could not leave my garage. I forgot having the smartkey function turned on can drain the battery and it was indeed low. Put it on an 8A charge for several hours and it was fine again.

Then a couple days later, as I was leaving the post office it did it again. I checked the battery and somehow did not have the negative cable at the post tightened completely, tightened it and it was fine again.

This morning it did it again. But then I discovered something. There was 12.5v at the battery itself, 12.5 volts at the jumper point under the hood, and 12.4 volts at the headunit when going into the diagnostic menu, but my OBD scanner showed only 11.5 volts at the port, and when I checked the voltage at the transmission control unit, it was also only 11.5 volts as well.

If I remember correctly, the p-lock error can also occur if the voltage falls under 12.1 volts.

I dug up the wiring manual and checked both ground locations for the TCU and both were fine, no resistance or rust/corrosion.I thought a bit of corrosion at the connection was causing this, but cleaning it didn't fix it.

I'm just disappointed at myself because I'm good with cars, heck I even rebuilt the motor in this thing myself, but there over a dozen computers in a Gen2 Prius and hundreds of feet of wiring, and dozens of added failure points from all that.

I even put a booster pack on the battery hoping it would trick the TCU, but that didn't work either.

I'm not sure what's causing a voltage loss of 1 volt going into the computers, but it's hot as heck outside and I spent 4 hours sweating my butt off and made no progress.