Prius Battery Replacement (GenII) Like you've never seen - NEW Cylindrical Cells

I just saw the next battery shipment isn't due for a month, and with my battery overheating I'm afraid to drive the car. The cooling fan comes on pretty quick after the car is started. Maybe I'll just do a diagnostic, find how many cells are bad, and if it's just a couple, go ahead and rebuild the battery with used cells, and then order one of TK1Toaster's kits at my leisure.

 

I'm brand new to code reading and such, my mechanical experience was mostly with really dumb cars. The triangle etc go away when I disconnect and reconnect the 12v battery and stay off, for about a minute or less after startup. The screen looks pretty normal except for the depth of discharge of the battery and rapid recharge. The ICE is running immediately on startup of course. I will likely use the prius daily to keep it charging for short trips only.

Thanks for the tip about the fan.

 

I'm brand new to code reading and such, my mechanical experience was mostly with really dumb cars. The codes go away when I disconnect and reconnect the 12v battery and stay off, for about a minute or less after startup. The screen looks pretty normal except for the depth of discharge of the battery and rapid recharge. The ICE is running immediately on startup of course. I will likely use the prius daily to keep it charging for short trips only.

Thanks for the tip about the fan.

 

I'm in the process of putting NewPriusBatteries in my 2004 Prius. First time the battery pack has been out of the car, but I guess not too bad since it has about 190K miles. Things have gone well so far, but I'm taking my time and taking notes and lots of pictures so that I can get it all back together. I did run into something unexpected when I took off the main cover. Attached to one of the upper tension rods is a welded on bracket with what I assume is a temperature sensor. Being a Gen2 I was anticipating there being three sensors on the bottom of three of the modules, but I wasn't expecting this one on the top. It looks like I can swap out the modules without disturbing this upper sensor or its wires, but I was more curious what this is and maybe I'll only find two sensors on the bottoms of the modules.

Through some more searching I found another reference to a 4th temperature sensor that apparently was only on the Gen2. I wasn't expecting it, and was sure that it wouldn't be in the way. I was just hoping to understand the design a little bit better. I guess that this 4th sensor was intended to monitor the air over the batteries after the cooling fan blew the air through them. It's also furthest from the fan, so the airflow at that end of the pack was probably the lowest. I guess Toyota decided that monitoring the temperature of the batteries themselves was a better method and dropped this 4th sensor from the Gen3 models.

 

There's 4 sensors. NPB recommends mounting them all on the top. Please see picture.

In my NPB install I mounted the temp sensors last all on the top. Upon disassembly i took all sensors off including the one your talking about and unplugged the temp harness from the ecu and put it aside Being careful with it. They note a few times be careful with the temp sensors.
There temp mounting clips were a little confusing to me at first but figured it out.
Here's pic of one mounted.

Also look at the 2 plugs in the battery ecu box closely make sure theirs no corrosion on the plug pins and also take the ECU pcb out of it metal case and look at it closely too for any kind of corrosion around the pins both inside and out. I was lucky mine was pristine. Many seen on this site were corroded.

The battery safety switch harness required a little offset bending of the bolt tabs too. Please see picture.

Been a few months since installation and running perfectly. Good Luck!

 

Thanks for the suggestions, and definitely the photos, they will be of great help. I was very careful with the temperature sensors on the bottom of Modules 1, 14, and 28. I also was careful with some modules between those (I didn't pay attention to which ones they were) but they had clips that were retaining the temperature sensor leads. Probably not as delicate as the sensors, but didn't want to put stress on the leads either.

I had seen another one of your posts where you recommended checking the connectors, and opening the ECU case and checking the PCB and the interior of the connector pins. I'll definitely do that. I did have a lot of corrosion on the terminal nuts, but it was on the surface and underneath as well as the bus bars looked pretty good. I wonder if the surface corrosion was due to the dissimilar metals?

I'm ready to start putting in the new modules, so I guess I'm past the midway point.

 

It’s easy to ohm out the sensors with the sensor harness unplugged just shove 2 sewing needles in each sensor lead pair at the plug there all like crap I don’t remember now 2000 ohms I think but there all identical ohms.
Good test because if one sensor goes open the battery will fail. There easy to damage I guess,
Do it last.

On mine the corrosion was not to bad just basic corrosion around the nut. Luckily the NPB cones with all new harness’s and hardware.

 

I was extra careful with the temperature sensors, but I'll check them for continuity to be sure I didn't break something. Do I recall correctly that you put the temperature sensors on the top like it is recommended, but that you needed to put the end ones on #2 and #13 because of the length of the wires? I wondered if that might be better anyway since the modules on the ends might have better cooling being more open. Seems like a better average might be taking the temperature in the middle and one module inside each end.

Agreed that the new hardware and harness are a good addition to the kit.

[Edit: I just reviewed your photographs again and it appears that you were able to get the sensors on the end modules.]

 

I was able to put them where they specified on the end modules plenty of length.

From what i understand from there manual the sensors since they are not in the airflow underneath will show hotter temps and make the fan run one more speed faster but you still may not hear the fan. faster fan=better cooling.
I say one more speed as I have not been able to hear the fan.

Have not listened to the fan inlet after a long run. I will though.

 

I think that I heard mine one time before on a really hot day. Recently though when the battery pack started causing codes, the fan would run at high speed until I cleared the codes. My understanding is that is what the system will do if there is a battery code, independent of the actual battery temperatures.

I've seen postings about using Torque Pro to set the fan speed. I'm still not clear on whether it's just until you shut the car off, or if it somehow retains it. When I tried it, I could get the fan to go up to high speed, but the next time I started the car, it was back to normal operation. I'm not sure that I'd want it running at Speed 6 all the time, but wouldn't mind a mid-range speed.

 

The problem with setting a lower speed, it locks the system out from setting a higher speed if it deems it necessary - say for example the ECU detects the battery temperature is climbing too high for its liking.

 

Makes sense. Hopefully someone will figure out how to set a lower limit speed and let the ECU increase it above the lower limit. I guess another alternative would be if the speed of the fan could be boosted across all speed settings. Probably not possible without redesigning the fan.

On a related subject, I was planning on removing the fan and cleaning it as others have done. I think that I'm suffering from disassembly fatigue and don't look forward to removing the fan. I'm not sure about the other Generations, but for the Gen2 it's mounted by the passenger wheel well and looks like I'll have to remove more ducting to get it out. I can look into the discharge port and can see the fan wheel and it looks pretty clean, not the dust encased mess that it sounds like some people have experienced. I guess I'm wondering if other people have inspected their fan and have found it to be no more than a little dusty.

 

I don't know why some people seem to get fixated on the fan speed, it seems to work just fine.

If you have been able to inspect the fan and it looks like it doesn't need a clean, then put off for later. I'd inspect it regularly and clean as required or if you happen to have the back disassembled for the HV battery or suspension, do it then. It is not too hard to remove the fan itself once you have the trim and the exhaust tube removed. Three pop-pins as I remember.

 

Thanks for the suggestion. I know that I should take it out and inspect it properly, I'm just accumulating a collection of parts in order to get the HV Battery out and I've either grown tired of disassembly, or I have this fear that I'll not get it all back together. Unfounded fear though, as I've taken lots of notes and pictures, so I'm sure it will all go back together without too much difficultly.

 

If you have an Android smartphone, an app called Hybrid Assistant can monitor and automatically control your fan. You can also set the lower temperature at which it references.

Hybrid assistant is a good overall app to use because it gives you visual indications of what your drivetrain is doing as well as temperatures of a lot of other systems

 

Having the sensors on the top of the modules does seem more logical. I've got the new modules in place and have found that like you had said, the wires are long enough to reach both ends of the pack. I was thinking about it though and wonder if it wouldn't be better to have them on Modules 2, 7, and 13, instead of Modules 1, 7, 14 anyway. In one of the previous posts, @2k1Toaster noted that in the Toyota packs, it was unusual to have failures on the end banks. It seems that they have better heat dissipation and don't overheat as often.

(Side note, my pack had failures in Bank 1 and 7. However, when I got the battery out, the weak module in Bank 1 was not the one on the end, but the one just inside, so it did have batteries on both sides of it.)

 

8AA I don’t know about positioning the sensors differently than where they want them.

I do know this is a very well engineered kit that goes together perfectly so theres a lot of R&D involved that I
personally would not second guess.