Problem: red triangle and brake warning lights, car! and battery icons on screen

I haven’t found a post with my combo of warning lights, so I thought I’d ask what it might mean in hopes someone could help me out.

I have a 2005 Prius, Basic trim, smart key, 205,674 miles.

At startup, I Have the red triangle with "!" and the brake ((!)) warning lights on the dash, and orange icons of a car with a ! and a rectangular battery in the MFD (screen). the ABS or VSC warning lights are NOT on.
When I start the car, the MFD reads “Problem” at the top before displaying the icons.




This just started randomly the other day when my partner turned the car on. We drove it a little and didn’t notice anything out of the ordinary with how it drove, braked or behaved.

I don’t have any error codes to post yet – my car was left open one night and someone stole my OBD-II reader. I just realized this when I went to look for it, and another is on the way, but I don't have it yet. So I tried to read the codes the old-fashioned way using the blinking warning lights (by shorting pin 4&13 on the OBD-II port). Unfortunately nothing blinked out a code to me – the brake warning light just blinked fast continuously.

Does this mean the generic OBD-II reader won’t help either? Think I should I get a Mini-VCI cable with techstream to really know what the errors are?

I disconnected the 12V battery to clear codes, etc and the same error indicators came right back.

I checked the 12V battery. It is old (replaced Aug 2014 [7.5 years ago now]), and voltage does fall to 11.7V with a load according to the MFD’s diagnostic mode. I’m thinking this could this be the problem, but as I said, I can’t find this combo of warning lights on any other forum post, and last time my 12V battery was dying back in 2014, symptoms were different.

I moved to a new city recently and since then have been driving it almost every day, but on much shorter drives than before, so wondering if that’s what pushed the 12V over the edge. I guess it should be replaced anyway, but I'm not sure I want to spend $220 on it if there’s some other big problem that might spell the end of this now venerable vehicle.

FYI I replaced the hybrid battery pack less than a year ago (January 2022) when a couple of cells in my original started failing. Used a reconditioned one from a company in CA, where I happened to be at the time. Gas milage also has been good lately - between 42 and 48 in the city with a lot of stop-n-go.

I’m about to take her on a drive from New Orleans to Pittsburgh in a couple weeks, so I’d like to make sure she’s safe.

Thanks so much in advance for any guidance!

 

Update:
I replaced 12V battery, which was due anyway, but that didn’t help with the errors.

I pulled codes with a generic OBD-II reader and got P0A08 and P0A09.
DC-DC converter circuit malfunction and DC-DC converter circuit low… Maybe an inverter problem?

When I cleared the codes they came back immediately. Not the next time I started the car, but like one second after I cleared them.

If any one has any thoughts, would be super excited to hear them. Thanks so much!

 

Thanks so much for the help and pointers! Reading through the service manual procedures right now.

 

OK - I followed the service manual instructions for P0A08, and quickly found that the little 5A mini fuse in the Fusible Link Block by the 12V Aux battery was blown. Replaced it and reconnected the battery and all codes and warning lights are now gone!

So that was the easiest 'fix' ever, but I'm wondering if it is actually the solution, or if I just treated a symptom of a deeper problem that caused that fuse to blow… I'll update here if I find out anything more.