Brake light, (!), ABS, VCS lights all on

How many miles on the car and how old is the 12 V battery?

I believe you have one (inverter coolant pump dead) or may be two (12 V battery on last legs) problems with your car.

You need to test the battery after the car has sat off for 3 or more hours to ensure any surface charge dissipates*. This would be the resting voltage. You then need to put the car into ACC mode (one press of the start button with foot OFF the brake), turn the headlights on and then measure the voltage again. The voltage should settle to a constant level after 10-15 secs and this is the voltage you should record. If the voltage does not settle but keeps dropping, let us know that too. This is the voltage under load. Stop this test if the voltage drops below 10.5 V.

Notwithstanding this, the reading of 12.3 V "or something", is too low and you should immediately put your battery on charge for 12-16 hours using a smart charger suitable for AGM batteries, if you have one. After this time, take it off the charger and let it sit for 3 hours to let the surface charge dissipate* then repeat the above tests. Let us know this second set of readings.

Hopefully, it is just your 12 V battery being in a poor state, but most likely your 12 V battery is due for change.

*Alternately you can put a load on the battery for 15-30 sec to dissipate the surface charge.

Sometimes a bright light behind the reservoir can help, but if you see no movement of fluid, your inverter coolant pump will need replacing. The symptoms of of this are as you described:

If the inverter coolant pump has failed, the dash warning lights will come back on after 10 or so mins running in READY mode after the car has been off for a while and you clear the codes. Obtaining the DTC's with Mini VCI will confirm for sure.

Let us know how you get on.

 

The thing to bear in mind, if your 12V battery is in poor condition, there can be spurious DTC's thrown, so you need to establish the state of that ASAP, and if it proves to be bad, replace it straight away to avoid chasing down red herrings.

Secondly, you need to establish whether there is or isn't movement in the inverter coolant reservoir ASAP to establish whether your inverter coolant pump is working or not as it is not good to drive on a failed pump. You could end up with an additional couple of failed parts, each in the realm of 4 figures to replace with new parts.

 

The inverter coolant pump will run whenever the Prius is IG-ON or READY. So just make the car READY and look at the reservoir. If you don't see fluid turbulence then either the coolant pump is not running or air remains in that system.

 

Just in case you are not sure where the inverter coolant reservoir is here is a pic:

 

You haven't said to what your test relates. I did asked you to take two measurements: a) resting and 2) under load. Then charge your battery and repeat the tests. Which does 12.03 V represent?

 

That's ok. Did you fully charge the new battery before installing? What are the resting and load voltages of the new battery?

 

Do you have a battery charger? If you don't I'd get one (Smart charger with capability to charge AGM, presumably your new battery is an AGM) and give your new battery a charge up to full. This is for the sake of looking after your battery as at 12.5 volts has probably sat around on a shelf for a while.

Yes I looked your Techstream images, and that is why I got you to focus on the 12V battery first. The Bxxxx codes can be ignored for now as they will not be contributing to your warning lights.

So are the C1256 and C1391 the only codes now? If they are then that is good and they are probably what you need to concentrate on. $1,000 is not too bad for a problem of this nature.

Were you able to confirm movement of coolant in the inverter coolant reservoir?

Here is a post where our knowledgeable member Patrick Wong comments and both the above trouble codes are mentioned.

Early failure mode on brake hydraulic boost pump

My ability to help you further ends at this point, but hopefully @Patrick Wong or others will be able to chip in with their thoughts.

All the best with the repair.

 

1. I agree that your 12V battery needs to be fully-charged now. Upon installation, the new battery was at 50% discharge. A new fully-charged AGM battery should measure 13.0V. A discharged battery will measure around 12V.
2. However, the low battery voltage is not the cause of C1256 and C1391. Yes, the brake actuator assembly needs to be replaced.

Since you have Mini VCI it is feasible for you to DIY install a used part which you can probably buy for ~$300 or so on eBay. The brake actuator is mounted on the firewall, you have to remove the cowl tray that the windshield wiper motor sits in, the inverter and the cabin heater core coolant pump for access.

This is a pretty big job. If you think you are up for it then you can obtain repair manual info at techinfo.toyota.com
Make sure you have the correct tools, for example you need the correct slotted box wrench to remove the hydraulic brake lines from the brake actuator assembly. You do not want to damage those lines. You also need to observe the safety precautions associated with removing the high voltage cabling from the traction battery to the inverter.

 

congrats!

 

That is good news, I hope you have many miles of trouble free driving.

Job well done.

 

Excellent thread... Especially, Dolj posted the picture with text described the Inverter Reservoir... This is how we have documents in High Tech places. Thanks