Does this sound like a 12 volt battery problem?

yes.. weak 12v. i tend to Always turn the car on when draining energy, or else you're likely to kill the 12v.

i'm not running on the oem battery. i'm using a jump box (not designed for this purpose) i leave all interior lights off.. when i park the car i turn the AC, and other power consuming items off. this insures i never get that message while starting the car.

 

The message about the transmission frequently is associated with a
weak 12V battery. The typical service life of the battery is ~4 years.
Extreme cold and hot conditions shorten that. If you've ever had to
"jump" the battery, it's life is further shortened.

Getting a new battery would seem to be in order.

As a side benefit, lots of folks report a significant jump in MPGs with a
new 12V battery, sometimes as much as 10 %. :rockon:

Hope this helps.

 

My Prius is a 2008 and I replaced my 12 Volt battery because of poor mileage and it was at the failure point in the diagnostics. I did not want my Wife to be put through any of those weird things like those you just described. My mileage went back up to normal and no odd happenings manifested themselves.

I put in the Optima and Kit.

Bob

 

It does sound like your 12v battery was discharged at that time. It may or may not need replacement, but if it cannot hold a charge it is time for a new one.

Have you ever drained the 12v battery (e.g. left the door ajar over night)? Each time this happens the battery gets weakened.

Do you do a lot of short trips? If so the 12v battery never gets fully charged up as the "constant voltage" charging system (at about 14 volts when your Prius is in "Ready" mode) in your Prius charges the 12v battery at a slow rate to avoid overcharging it.

You can check the state of your 12v battery and the charging system using the MFD. The procedure is documented at the ElearnAid web site (They sell a more robust battery for the Prius - The Optima Yellow Top). Go to:
12 Volt (12v) Toyota Prius Auxilary Battery for 2004, 2005, 2006, 2007, 2008, 2009 and 2010 with installation kit
The MFD battery test procedure is near the end of that page.

JeffD

 

I agree that your car needs a new 12V battery.

For future reference, please avoid leaving the car IG-ON (where the dashboard warning lights turn on) for any length of time. The drain on the 12V battery is quite heavy in that operating mode.

If you want the air conditioner to be on, then make the car READY.

 

Have 2009 Prius with about 181,000 miles on it.Yesterday(March 14, 2020), was driving on 2 lane highway, suddenly started losing power, all dash lights came on like a Christmas tree(including red triangle), and speedometer light disappeared, was able to pull off road. Tried starting would not do so, could only put in "park" or "neutral", so finally had call to tow truck, to take to garage. In January of this year, went ahead and replaced the 12v battery(had about 8-9 years on it), with a new "Yellow top" from AutoZone cost me around $250.00, so at least battery will still be under warranty. I suggested to tow truck/ garage owner to check the 12v battery, my gut tells me new battery is fried. Just wanted to share my recent experience

 

welcome!
more likely the inverter pump or something else

all the best!