2007 Prius - 12v Battery Issue (Please Confirm Diagnosis)

It is very unusual to hear that the POWER LED light is showing a green color (which signifies ACC-ON mode) while the car is actually in IG-ON mode (where instrument panel warning lights are on, and the POWER LED light should be amber.)

If the energy monitor display (MFD) remains on, then the car has not turned off, and the 12V battery will quickly become discharged.

I agree that it would help to measure voltage at the jumpstart terminal with a digital multimeter and also to press hard on the BRAKE pedal when attempting to start the Prius.

Check the AM1 and AM2 fuses. If those fuses are OK, there may be a problem with the ACC, IG1, or IG2 relays or the power source control ECU may have failed.

The basic issue seems to be that the Prius will not become READY and that the power source control ECU is confused as to what operating mode it is in. The four possible modes are IG-OFF, ACC-ON, IG-ON, and READY. (The POWER LED light will be off in IG-OFF and READY modes.)

It should be possible to shift between the first three modes simply via repeated presses of the POWER button (leaving the brake pedal alone.) Then when the brake pedal is pressed, a press of the POWER button should make the Prius READY from any of the other three modes.

 

This is not correct. The ECUs will reset when they are powered down, which will happen while the old battery is disconnected.

Nevertheless I am glad to hear the car started this morning. It sounds like you did not drive it today?