Hybrid battery replacement using a new Toyota battery

I need to replace the hybrid battery in my 2007 Gen 2. It’s at 188,000 miles and the panel just lit up. The diagnostic codes make it clear that the hybrid battery is faulting.

I’m considering an option that I haven’t seen mentioned on PriusChat: Replace the battery with a brand new Toyota pack, and do the work myself.

Web search for the part G9510-47031 reveals that the Toyota list price is $1950. That seems like a good deal when compared to prices for remanufactured batteries. A little more searching and I found it for $1600 at a Toyota dealership a couple hundred miles away. This is looking promising.

The Question: Does buying this part G9510-47031 give me a drop-in replacement for my failing battery? Or is there more work to be done -- maybe transferring components from the old pack to the new pack before installing the new battery?

 

Thanks bisco and ericbecky.

I’ll keep this thread updated as the story unfolds.

Right now I’m on hold, waiting for the diagnostic trouble codes (DTCs) to reappear. I cleared them yesterday. Here’s why.

I replaced the 12V battery. I saw comments somewhere suggesting that a weak 12V battery could cause the P0A80 code to appear. That seems superstitious and far-fetched to me, but OK, I’ll try it. My 12V was due for replacement and I’ve had the new yellowtop on hand for a couple weeks. That’s done. Then I cleared the DTCs and we’ll see if my P0A80 comes back.

I’ve also seen people say that the hybrid battery cooling fan could cause P0A80 if it’s dirty or not running right.

Yesterday I stripped out the interior to clear the way for the battery work. With the passenger-side trim out of the way it was easy to detach the ductwork so I could see the guts of the squirrel cage fan. It’s a little dirty, dusty, but nothing like the clogged up ones I’ve seen in pictures. It can’t be dirty enough to be the problem. It still could be running poorly though, and that brings me to the topic of Torque Pro.

I’ve had Torque Pro on my phone for a while. I bought a cheapie OBD2 Bluetooth dongle and it works OK for reading speed, RPM and other ‘normal’ readings. It doesn’t seem to transmit the Prius-specific data like module voltages and fan speed. I want to monitor and maybe control the fan speed in order to rule it out as a cause for my P0A80 DTC.

I ordered a PLX Kiwi 3 Bluetooth OBD2 device, $90 from Amazon. I chose that one because ‘usbseawolf2000’ uses that brand. He has an amazing writeup on it. (I can't attach the link until I have more posts on this site -- I'll edit later when I can!)

When that OBD2 device arrives I’ll try to acquire the hybrid battery voltage data using it. If my DTC gets thrown again that will give definitive evidence that I have failing modules. As soon as I have that proof I’ll buy the new battery core.

At this point I am totally sold on buying the new Toyota battery assembly. If swapping the parts like ericbecky says is not too difficult that is the best way to go for me. New battery modules (some people have claimed that Toyota batteries contain used/refurbished modules, but I just don’t believe it). New bus bars with no corrosion problems. New, new, new, all new.

I have a lot of respect for the people that go to the effort of pulling the battery and then replace a module or two. The phrase “whack-a-mole” is a good description for the problems they may face in the future. It’s a lot of work, with uncertain results.

I like the idea of replacing all the old modules with new cellpacks – the Newpriusbatteries business venture. But the price of $1600 is too close to the stock Toyota price of $1950 to make me go that route.

Refurbished batttery? Fuggedaboutit. That’s not a contender in this decision. Sure, my car is old. 2007 with 188,000 miles. But I want my next 5 to 10 years with it to be as trouble free as the last years have been.

My local Toyota dealer was not willing to do a price-match to the $1599 price from Metro Toyota of Cleveland, OH. But he’ll sell me the same battery assembly at the standard Toyota price of $1950. I might pay the extra $350, just to avoid two trips to Cleveland. One to buy the battery, another to return my old core, to get the core charge refunded. I don’t know how much the core charge is, but I suspect it’s in the ballpark of $1000.

It’s about 3 hours drive to get to Cleveland from Ann Arbor. Two round trips … 12 hours of driving, plus gas, plus cheeseburgers … yeah … I might be better served to pay the extra $350 to my local Toyota dealer. I can order the battery in the late afternoon and it will arrive next morning.

I asked the Toyota service desk what they’d charge to do the installation. They said $625. 5 hours of labor! That seems exorbitant to me. I’m not going to claim that me stripping out my car’s interior would save them a lot of time. There's a YouTube video (I'll edit later with the link!) showing a real pro whipping out a Prius’ interior like it’s nothing. What took me an hour takes them ten minutes.

But I bet it takes the Toyota dealer a LOT LESS THAN 5 HOURS to do the replacement. "Labor hours" are a convenient fiction. That’s why they call them stealerships. Just sayin’…

I asked another local business what they’d charge to swap batteries, and they just replied “No, thanks”. They didn’t want to get involved with a DoItYourselfer’s project. Fair enough.

Where am I now? My car is all stripped out and looks terrible. I’m waiting for DTCs to reappear, and getting ready to see if Torque Pro can show me the voltages inside my old battery pack.

I post back as the story develops.

This site has been a wonderful help. Thanks everybody!

 

The good thing about being wrong is, you learn something. Maybe my P0A80 code was due to my 12V auxiliary battery after all. I was skeptical about it.

I wonder why this didn’t occur in the dead of winter? Here are recent voltage readings from the MultiFunction Display diagnostics:

1/31/2019, air temperature -3F: Diagnostic 11.3V, car Ready 10.3V
4/5/2019 air temperature 60F: Diagnostic 12.3V, car Ready 11.9V, with headlights on 11.6

That battery looked pretty weak in the cold weather.

My hybrid battery’s module voltages appear to be fine according to Torque Pro and my new PLX Kiwi 3 OBD2 device. When discharging the voltages are in the high 15V to low 16V range, and the difference between the highest voltage and lowest voltage modules is about 0.3 volts. That sounds like my HV pack is reasonably healthy. Certainly there are no shorted cells. For now I won’t do anything to the hybrid battery.

I’ve also been curious about the hybrid battery cooling fan. I have not been able to get it to run. I’ve read a number of threads where people say the fan runs only when needed, based on hybrid battery temperature and vehicle speed. In chilly Michigan I’m not going to get the hybrid battery warm for a couple months.

A Youtube video (Google “2004 - 2009 Toyota Prius - Hybrid Battery Fan Test”) claims that by putting the car in “IG ON” mode this fan should run. Mine doesn’t. ("IG ON" is the mode you get by pressing the main power button twice, slowly, without having your foot on the brake pedal.)

Question: Is there an easy way to make that fan turn on, for a Gen 2 Prius? I’ve seen people mention some magic with Torque Pro, but I don’t find any settings which relate to controlling the fan. Can anybody give detailed instructions?

While looking at PriusChat threads about this fan I found that people have had corrosion in the connector which provides power to the fan. (Google “Battery Fan Problem - Can you help me save $600?“ for the PriusChat thread.)

When I changed my 12V battery I found it sitting in about an inch of water, so my car does have the typical body leaks which I’ll need to seal up when the weather warms up a little more. Sure enough, I have corrosion in that connector, on the two pins which people say are for the fan circuit. So I’ll be splicing / jumpering around that connector sometime in the next couple weeks.

The story continues...

 

Rats. I did the victory dance much too soon. My P0A80 code came back. Tomorrow I’ll order the battery from my local Toyota dealer.

I’m monitoring battery voltage using Torque Pro, and one module exhibits voltage sag, only under moderately heavy loads. The biggest voltage drop I’ve seen is about 1.2 volts. As I said earlier, mostly I’m seeing 0.2 – 0.3 volts difference between the minimum and maximum module voltages. So it’s a weak module, but not a shorted cell. I’m still driving the car, but very light on the accelerator pedal.

ericbecky, in post #3 above >> And please buy an inch pound torque wrench for installing the nuts on the high voltage contactors and modules. Don't be lazy and think it is ok to simply guess at the tightness for such important components. Too tight, and you risk stripping or breaking off the post. Too loose, and you risk having acting and a fire.

Got it, thanks. I do have an inch-pound torque wrench and some 1500VDC electrical safety gloves on order.

Here are some VERY HELPFUL PriusChat threads:

• How to remove Hybrid battery quickly and easily (This had the 10-minute interior strip I mentioned in post #4)
• My P0A080 fault code and battery rebuild (fotomoto, who convinced me that playing whack-a-mole is not the way to go)
• Replacing the hybrid battery with a new Toyota battery (lots of good advice here)

Thanks ericbecky for all the posts you’ve made to DIY-ers working on their battery problems.

Hopefully my next post in a couple days will be “Job done”.

 

Hi terramir,

Sorry, no pictures, but I can offer you a thousand words.

Below, ‘front’ means ‘front of car’, and ‘back’ means ‘back of car’.

What you get:

• The battery assembly, including the base and top cover, with all the battery modules installed.
• The battery modules are already interconnected with bus bars in plastic carriers.
• The voltage sensing wiring harness at the front of the battery, already installed.
• The temperature sensor and wiring on the top of the battery modules, already installed.
• The temperature sensors (3) and wiring underneath the battery modules, already installed.
• The temperature and voltage sensor wiring is terminated in connectors which you will plug in to your ECU (computer) and to the current sensor.
• Two high voltage leads, one long and one short, which you will mount to the front of the battery pack.
• A new Battery Plug with its two high voltage leads attached, which you will install. I would have called this the Main Service Plug Receptacle, but Toyota calls it the Battery Plug. It mounts on the rear of the battery.
• Two special nuts which you’ll use when connecting the high voltage leads to the main relays in the upper subassembly.
• Four special nuts which you’ll use making the 4 high voltage connections to the battery pack.

What you don’t get:

• The “upper battery assembly”, which is a metal housing which carries the ECU computer, three relays, a large resistor, and a current sensor. This upper assembly holds all of the electronics on the driver’s side of the battery. You are expected to remove this assembly from your old battery and transfer it with all the electronics to the new battery. It mounts with 3 nuts that go on studs which are on the new battery base plate. I left all the abovementioned parts mounted to the assembly and transferred it all as a unit to the new battery housing.
• The air hoses which connect to the top of the modules. You have to transfer the air hoses from your old battery pack. My next post mentions a video which shows how to do this.
  
• My battery kit was missing the 10mm special nut (single-use-only) which clamps a shielding conductor (part of the longer high voltage lead) to the upper subassembly housing.
• My kit was missing two 8mm special nuts (single-use-only) which you’d use to connect the car’s high voltage wiring harness to the battery pack when you mount the pack back into the car.

Very roughly, here’s the story, after you've gotten your old battery out of the car and you have the new Toyota battery on hand.

Caution: high voltage can and will kill you if you do something wrong, even with the Main Service Plug removed. I am not advising you to do this work, and I’m not advising you on how to perform the work. Any time the modules are connected with their bus bars, voltages add up to potentially lethal levels. If you don’t understand what I just said, you should not attempt this work. Treat both the old and new battery packs with great respect and caution!

• Take the top covers off of both the new and old batteries. Now you're in High Voltage Territory, and it's dangerous, and I didn't advise you to do it.
  
• Disconnect the high voltage wiring from your upper battery assembly and disconnect the connectors at the front of the ECU computer.
• Unscrew (3) nuts which hold the upper battery assembly on your old battery.
• Transfer the assembly to the new battery and mount it with the nuts.
• Install the various high voltage leads and plug the connectors into the ECU and current sensor.
• Any time you make a high voltage connection, there’s a torque specification for the fastener. Use a torque wrench and do it carefully and correctly. (Thanks again, ericbecky!)

My next post will have more about "lessons learned".

 

Job Done.

A warning though: The high voltage battery can kill you. You do this work at your own risk. Don’t undertake this job unless you’re sure you can carry it out safely.

I am not a mechanic or auto technician – but I do have some electronics background and I understand the danger. I figured I could do it without getting killed, or letting my cat get zapped through all its nine lives.

I spent a lot of time gathering information on PriusChat and YouTube. I planned what I was going to do, and I worked slowly and carefully. Even with the main service plug removed, I used a voltmeter to check for high voltage as I worked. And even then I wore brand new high voltage gloves when working around the battery modules, which I suspect a lot of professionals don’t do. The less you know, the more careful you have to be.

End of lecture. Sorry to belabor it.

Resources I Found and Used
Videos:
This PriusChat post shows how to strip out the interior.

This YouTube video gives beautiful clear views and instructions on everything involved in working on a Gen 2 Prius battery pack. Major thanks go to Chris of Electron Automotive (and his cameraman!) for this work.


Documentation you need:
From clues in this thread by ‘wegortw’ I found the entire repair manual for 2004 Prius. Mine’s a 2007 – close enough! Google for “RM1075U” and you’ll find the manual online.

Google finds a web page on cardiagn.com. Scroll down and click into the link “Hybrid Control System”. It opens a PDF file which you can download. They even have a sidebar showing you how to download their documents. Wonderful!

The Hybrid Control System document has over 400 pages of everything you need to know to accomplish the battery swap. Don’t expect it to be organized in the best way for swapping the battery – you’re going to spend an hour or two in that document piecing together the story. But you’ll get beautiful exploded views, lots of torque specifications, and good specific instructions.

Special Tools:
I already have a lot of tools for doing my own auto repair. But I did buy these items:

• Tekton ¼” drive click-type torque wrench, $41 at Amazon
• Magid class 0 high voltage gloves, $51 at Amazon

Trivia:
#1: Face it – at some point you’re going to close the rear hatch when the 12V battery is disconnected. Google “prius trunk release from inside” and you’ll learn how to pop it back open.

#2: I checked the date codes on my new Toyota battery pack. All the modules were manufactured within a day of each other, and all in December 2018, so only a few months ago. This PriusChat post has an attachment that shows how to decode the date information printed on the modules.

#3: A Gen 2 Prius has enough cargo area to carry a replacement battery pack in the bulky shipping container that it comes in. You won’t have to rent a truck to schlepp the battery around if your Prius is still running.

#4: The core charge for the battery was $1350. This transaction put a $3417 hole in my credit card, but I should get the core charge back.

#5 I had to make a return trip to my Toyota dealer for hardware not supplied with the battery kit. See my previous post above.

#6 Being mistrustful, I loosened and re-torqued all the nuts at the module connections, where the copper bus bars connect between the modules. All 56 of them. Now I know they’re correctly torqued.

#7 Mostly the work is pretty foolproof; things only go together in one way. So aside from the high voltage danger, there’s not much to go wrong.

#8 Yeah, my back hurts a little. I’m a 62 year old guy, not in bad shape but I’m sure not an athlete. “Lift with your legs” is great advice, but when you’re 6’2” crouched inside a Prius pulling the battery out or putting it back in, you can’t lift correctly. Aside from those hard lifts, I had help moving the batteries around. Thankfully I’ve got a tough girlfriend who’s a gym rat, and she was happy to help.

#9 Yay … job done.

 

@ericbecky: You're right, I forgot to mention the small foam baffles/cushions. They have self-adhesive strips on them, so you peel the cover tape off and press them in place. There's also a plastic fitting on the top at the driver's side end of the battery assembly which you transfer from your old battery to the new.

That steel end plate on the passenger side of the battery: opinions vary about whether to leave that part on the car when you pull your old battery out. The 10-minute video of pulling the battery showed leaving that end plate in the car, so that's what I did. Yes, the small white plastic plug/clip had to be removed when unfastening the end plate, so I saved it with other hardware and reinstalled it when the new battery went back into the car.

@Mendel Leisk: You're right about the warranty. The people at my Toyota dealer explained carefully that if I just bought the battery kit I'd only have 1 year warranty, but if they installed it I'd get 3 year warranty. That's consistent with what I've read elsewhere on PriusChat. My view on that is that there's SO MUCH advantage in getting all new modules and bus-bar interconnects (re: corrosion) that the new battery is likely going to be trouble-free for a lot longer than 3 years. Other things could go wrong of course which might have been covered (I'm not sure!!) by the 3 year dealer install warranty. The ECU computer or a high voltage relay could fail. The ECU is a $750 part if I recall correctly. I'll solve those problems if and when needed --- but I'm betting I'll be fine, battery-wise, for as long as I want to own the car. And that's probably 5 to 10 years.

I returned my old battery core the day after I picked up the new battery kit. No trouble.

I've put about 150 miles on the car since starting it up for the first time with the new battery. No troubles, no codes. It's a thing of beauty.

A back-of-the-envelope calculation showed that I've saved over $5500 just in reduced fuel costs in the 7 years I've owned my Prius, as compared to my 24mpg much-loved Volvo 240. So even after spending a little over $2000 in battery kit and tools, I'm comfortably ahead of the game. The Prius has also saved a money on other running expenses. I've only had the brakes worked on once, and it was just a pad replacement. I've not had to change the exhaust system at all, and it's a high-mileage car. Much better than periodic exhaust maintenance costs on a regular car.

So far I seem to be getting about 10% lower gas mileage after the battery install, 38 mpg vs expected 42 mpg. I don't know whether that will correct itself in time. Maybe the engine control computer needs to re-learn its fuel injection mapping. Anybody have an opinion on that?