DIY Prius HV battery rebuild

Well Mike, now you know you're problem. You can simply change out that module and you may get lucky and get years more use out of the battery. You could balance charge all modules and hopefully get years more use but, the best fix is to buy a new battery from Toyota and replace it. The cost is about $2000

 

This is a classic example that voltage is not a good measurement to determine cell health (although voltage under load is better). Obviously one of those modules is fluctuating enough to throw a code. I would replace both and maybe even the modules on either side of them. A weak module becomes hot and has likely transmitted heat to those other modules. This will weaken them as well.

 

What's your method for rapid HV pack disassembly?

I learned to put a couple of long 2x4 on my workbench. I remove the top cover from the pack and then remove the busbars from the side of the pack with the thin wires that go into the battery ECU. Next I flip the modules upside down so they are resting on the 2x4's. Then I remove the 28 bolts that attach the sheet-metal lower tray of the HV pack to the module. I undo the 4 tension rods that go from end to end only when I am changing out individual modules. I immediately put the 4 tension rods back together. Now I'm ready to do bench testing/cycling etc. I don't reattach the lower tray until I'm satisfied that the pack is ready to put back into the car.

-EB

 

Amazing that they both still measure 8V. Can you tell which of the 2 is leaking the fluid?

 

Do you recall any liquid leakage or corrosion near the busbars the first time you took apart the HV pack?

I guess I'm lucky but NONE of the modules in my pack had any signs of leakage.

 

I have to call urban legend on this. I have never seen a code from a .3 voltage difference. I have never seen a post from anyone that has seen a code thrown from a .3 voltage difference. The official Toyota repair manual recommends replacing a pack that has greater than a .3 volt difference while running a charge and discharge test.

I used to parallel modules to bring them to the same voltage and what I thought was the same State Of Charge. Paralleling modules will bring them to the same voltage but NOT the same SOC. I have tested this.

There is disagreement on the value of cycle charging and discharging modules. Kiwi is the champion of the opposition and I and others agree that the best you can do is measure what the modules have left and use the best of them. The mainstream opinion on Prius Chat is that balancing is the cure all to everything. I try to not use the "B" word. It gets thrown around so much that it is undefined.

I agree. What is really needed is a consistent measure of capacity at a high rate of discharge. The other important test is self discharge. Any module that can not hold at over 7 volts for months or years is junk.

Again, this is against the majority opinion and what the Toyota repair manual claims but the module count starts opposite the battery ECU.

Clean those battery terminals! Everyone gets so worried about the nasty copper bus bars that the battery side of the connection gets over looked. I use 1/2" squares of 3M green scrubbing pads. Clip a slit in the pad so it can slip over the battery stud. Spin the pad with a small socket and cordless drill. I use a junk sock and filed some teeth into its face to give it some bite against the pad.

After the cover comes off I immediately remove the rear bus bars without the voltage sensing wires. Remember, high voltage is present until all the bus bars are removed from one side of the pack. Next the front bus bars are removed. Then disconnect the white plug from the ECU and the white plug from the current sensing ring. Remove the two 10 mm nuts holding the white plastic end caps to the case bottom. Now flip the battery upside down and remove the 28 mounting bolts. Now the case bottom can be lifted off the modules and tension rods. It is much easier to disassemble and reassemble the modules into the tension rods without the case connected.

I have lots of extra white plastic end caps. Two end caps with four 5/16" X 6" bolts will hold 5 modules in compression. This is handy for working with a smaller and lighter group while charging or discharging.

Brad

 

The bad news is that the warning lights are still on because I broke one of the temp sensors that clip on the bottom of the cells and now the car is throwing a P0A9E... does anyone know if those senors are easily replaceable? Both wires broke off right before they went into the plastic clip that holds the thermistor

The sensors are easy to replace. You just have to take every thing apart again. The sensor harness includes the three snesors on the bottom, one on the top, a big white plug into the computer, and one more plug into the current sensor. I have lots of these sensors. Send a PM if you want one.

Brad

 

My Techstream counts blocks from the fan side of the pack.

 

You can use a 5 kOhm resister to replace them. If you damaged the one at the end of the pack, you may be able to service it without taking it out of the vehicle.

 

To help, not to criticize:
Old thread but should be noted that cordless drill should NEVER be used on a series electrical circuit, or any electrical termination really.. Not a consistently accurate device.
My money on drill error for melted parts. Sounds like a burning of the vehicle to the ground was narrowly avoided.
New readers of this thread suggested to:
Get the nuts finger tight, then use an inch pound torque wrench to tighten every nut to [the] factory specification. I would go back over all at least twice.
If Terminals Corroded The cleaning of terminals is mandatory, use wire brush and anti-corrosive/dielectric grease before reassembly.

 

can you explain how to do this parallel test? and what is needed?

 

The parallel "test" is unnecessary. All this does is equalize the static voltages of each module. Module load testing and self discharge are the important things to check. As long as module voltages are within 0.2 volts of each other equalizing the modules in parallel is really just wasted effort. I didn't equalize the modules in parallel when I did my DIY pack repair and the pack was fine immediately after the repair and six months later.

 

I just bought the app and im borrowing a friends obd2 reader and its hooked up via Bluetooth .... I don't see or can figure out how I can monitor the 14 individual block voltages? can you tell me how to do this

 

Assuming G you have an android phone/tablet....
Step one, for under $20 purchase and install the Torque Pro app.

Step two for under $20 buy your own ELM 327 Bluetooth OBDII READER from Amazon.

While you are waiting for the Bluetooth device to arrive set up a screen in the Torque Pro app that shows all 14 battery blocks.

When the Bluetooth device arrives, plug it into the car, pair it with your phone/tablet, then read the data.

 

borrowed a friends OBDII reader and last night it showed block 6 had way more issues then block two ... so being the DYI dope I am ... I replaced the 2 cells in block 6 from my spare cells I had ... put it back together after a few hours ( don't do this in the heat the cells expand ) and now im getting a code P0AAC and thet is saying one of the sensors that detects the heat is bad or "off" the cell ... now my dashboard looks like a xmas tree.

 

Go back and check the actual sensing wires for corrosion. Especially where the crimp connections.

You still will want to get your own reader since you will need to check in your battery status and other parameters on a regular basis.