Dead 04 Prius

At the very least you need a new 12 V battery. You have other issues more than likely, and you will be able to reliably diagnose those much easier with a healthy 12 V battery.

If those 14 voltages are the block voltages of your HV battery, you need to replace block 1 (2 modules) with 2 modules that closely match the capacity of the other remaining 26 modules. Then charge and balance the whole battery and see where you are.

 

The 12V was at 9.00V ON And 9.51V OFF.

Straight out of the gate, I'd hope your mechanic was all over the above information. That battery needs to be charged, not exceeding 4 amps if it's an original Toyota agm battery. If it's an aftermarket, charge rate will depend on battery style. The 12v battery provides power to boot up all the computers in the car. The Gen 2 Prius has 14+ ecus, so it's extremely important to have proper power on the 12v circuit. Computers don't work well if they don't have the proper power supply.

The jump/boost allowed the computers to boot up, but unless you allow the car to sit in "Ready" condition for a day or so, it had no chance, whatsoever, to actually charge your 12v battery. Once you turn the car off, you're back to square one, with a dead car.

Your HV battery has 28 individual 7.2v batteries (modules) inside. These are usually around 7.5-7.7 after sitting unused for a while. The ecu monitors them in groups of 2. Every group of 2 is called a block, so there are 14 blocks. The battery ecu has one sensor on each block to monitor the overall health of the battery. Each sensor registers the combined voltage of 2 modules. Block 1 is the two modules furthest away from the ecu.

The info the mechanic got while the car had good power on the 12v circuit included-----V1 10.03 and all the others are in the 16v range.

The 16v is telling you the HV battery was recently (or is currently) in a 'being charged' condition, because that's the only way you could ever have that high of a voltage if the car has been sitting for months.

Every battery ever manufactured has some amount of self-discharge, which typically gets progressively higher as the battery ages and cycles. The 10.03v is telling you that one or both of the modules in Block 1 have self discharged or failed while the car was stored. (There is always the slim chance that a different problem is causing the low voltage reading.) The possibility does exist that you can fire the car up, force charge the HV battery, and it will recover Block 1 well enough to let you start driving again. Self discharge problems in individual modules can sometimes be overcome just by driving the car often, preventing the self discharge from being enough to trigger a code. Even if force charging works, at some point, it would be in your best interest to replace one or both modules in block 1.

Think of your HV battery as having 28 water jugs, each with a different sized hole in the bottom. None of the jugs will go empty if you keep adding water to them faster than it's draining out. Driving the car every day, allowing it to charge the HV battery, is like adding that water, but eventually, one of the holes just becomes too big and it's time to replace that jug....

 

After you charge or replace 12v... One of the two modules in block #1 has a self discharge issue/bad cell. If you lived near me I'd do a full charge & balance of the pack and see how many error codes go away after than and then replace the bad module and replace all the corroded hardware and then recondition the pack and you'd be good to go for anywhere from 3 months to 3 years.

 

Olympia

 

When the combination meter goes dark holding the power button down for three seconds will shut off the car. The fix is to replace the combination meter.

The P0A84 battery fan codes is usually caused by a corroded white plastic wiring plug next to the battery fan. That plug can get wet from leaky hatch seals.

 

I would do those in reverse of that – cooling fan fix, combination meter, and HV battery. Retest the car after each fix.

 

Matt at Texas Hybrid Batteries is well known here and recommended. He has a good deal, get in touch and he'll see you right. Your car is a 2004, so also look into upgrading to the 2006-2009 CM and to do this you will need to replace your light cluster with one Matt can supply you. This will fix the 299,999 miles max limitation that the 2004-2005 had.

 

Please review post #10. It is VERY RARE for a Gen 2 fan to fail. There is a wire harness plug clipped near the fan that has corrosion problems. I've seen it in EVERY Gen 2 I've worked on. I typically clip the wires and buttsplice them together and use heatshrink to insulate them. I do this free for every customer that purchases one of my batteries. The one in the photos below has pretty mild corrosion.