Yellow Brake Warning Light

Yeah, I read that online too. It'll actually get to ready, but I have to put the fob in the dash and the hatch still won't open. I'll figure it out tomorrow.

 

Hatched opened without incident this afternoon. Turned car to Ready and disconnected the battery. 12v from positive to chassis. Left it at Ready and reconnected the ground. Still 12v from positive to chassis and 12v. from positive to negative. Turned car off, 11v from positive to negative.

So, inverter doesn't seem to be working properly. I think my last check will be to get some of the Pentofrost A4 and top off the system and see if that makes a difference. I'm not hopeful. If not, it heads to the mechanic tomorrow. It looks like there's a well respected Toyota and Prius mechanic here in Columbus named Tongda Auto. I think I'm going to try them rather than the dealer.

So, is an inverter change, assuming that's what I'm looking at, a DIY job?

 

I have an alldatadiy.com subscription which has the inverter replacement instructions. Not trivial, but something I think I can do. I do think I want to have it diagnosed by a professional first, however.

 

So, the verdict seems to be corrosion at the connector to the brake control power supply back, which is next to the 12v battery. The mechanic is going to disassemble the connector, thoroughly clean the pins and put it back together. The module itself looks good, I'm told, which is good as it's a $500 part. Plus, it seems the inverter and main battery seem to be fine as well. I'll know for sure tomorrow when they finish the work.

A bit frustrating as that's what I determined, but I was not able to get inside the connector to really clean it well.

 

A final update: Cleaning the contacts did not fix it, and they said the brake control power supply needed to be replaced, which they wanted another $500 to do (the part is $485, list, I believe). They verified that would correct the problem by swapping in a part from another Prius they had in the shop. I had already paid about $375 for the work to date ($95 of that was the diagnostic fee), which I have mixed feelings about. On the one hand, that's a lot for diagnosis & corrosion clean up. On the other hand, I now have a definitive diagnosis and there was no way I was going to be able to get inside that connector to clean it up.

Anyway, I did some quick searching and found used parts are plentiful on eBay for less than $50. At that price it's worth a try. So I declined the repair and ordered an eBay part for $24, shipped. It arrived Friday. It's cake to change - pull the cargo floor and lower tray and it's right there on the passenger side. Three bolts and it's out, 4 more to swap the brackets. Took me about 30 minutes and the light is now gone.

I'm still not convinced that my 12v battery isn't bad nor that I don't have an issue with the charging circuit, but I have no lights on the dash at this point so everything seems OK for now.