It might be time for a new traction battery....

nedim · Feb 15, 2015

jdcollins5 said: ↑

kc410 said: ↑

jdcollins5 said: ↑

If the difference between Max-Min is greater that 0.3V for a time delay it will be generating a DTC and stopping the car.
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Vmax-Vmin of less than 0.7V will not set a trouble code. When Vmax-Vmin goes over ~0.7V it will set a trouble code & cause the ICE to run continuously. The Prius is still drivable, even for long distances if necessary. I have encountered this situation a few times when my traction battery was failing.
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The Repair Manual says greater than 0.3v for a set time delay will set a DTC. Where are you getting your information?
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kc410 said: ↑

Lets see if I can answer these one at a time...

Thanks for the info. I started the car this morning, it did its normal warming and engine shut off... Where exactly in Torque you can see pending codes ?
ANSWER: a pending code will show up the same place as a fault code. In Torque its under "Fault Codes". after it checks for faults on its display page a pending code will "Pending Code" in front of it. A pending code never shows up on the Prius dash (at least it never did for me).

I did not see any codes in ScanGauge, Torque or Techstream ....
ANSWER: like above - in Torque hit "Fault Codes" & let it run - takes ~ 1 minute & it will display a page - any codes will be shown there.

Doing the test where you engage the parking break and put the car in reverse shows me Vmin-Vmax = 0.1 ...I can see that number change only if I am driving...
ANSWER: I have never done the "parking brake test".
ANSWER: This is going to be a longer answer (there is no short answer) - The Prius will only allow the battery to operate in the range of 40-80% SoC (State of Charge). The Prius will try very hard to keep the battery at 60% SoC. At 60% SoC the module pairs in my failing traction battery would still be very close in voltage, sometimes within 0.1V across all 14 pairs. BUT, below 60% SoC the voltage difference became very pronounced & the module pair with the weak cell would fall off very fast. Say at 55% SoC the battery might show 0.7V difference between Vmax & Vmin & below 55% SoC things got much worse. Here is the unexpected part - Going above 60% SoC was just as bad. Slowing down from hi speed to a stop would put a substantial charge into the battery. The module pair with the weak cell would soar in voltage compared to the other 13 module pairs. This has at times caused the P0A90 fault for me.

As I remember you did change the whole battery, right ?
ANSWER: yes
Why didn't you consider replace only a module ?
ANSWER: I did consider that. I considered it enough to purchase two HiTec x4 80 chargers & one HiTec 30A power box to run them (I have another HD 12V supply to run one of the HiTec chargers). With that I can do 8 battery modules at the same time. The problem is, even at the best the Prius will be out-of-service for 3-4 days at a minimum.
Then I found a whole traction battery - then had to build a new charger/discharger to cycle the whole pack.

And here comes my next question...
How can you tell which module is bad ????
ANSWER: by monitoring the voltages of the 14 battery module pairs. As the battery discharges most of the 14 voltages will track each other. Most likely you will see one of the module voltages dropping quite a bit below the other voltages. This module pair will point to two battery modules, either of which could contain the weak cell. Another way to find which module pair is weak is by monitoring the Torque pids "Block# min" & "Block# max". During discharge (<60% SoC) the "Block# min" will be the block with the weak cell. During charge (>60% SoC) the "Block# max" will (probably) be the block with the weak cell. Now you know it is one of two adjacent battery modules. You need to use a voltmeter to determine which module has the bad cell. I do not suggest doing this BUT in theory you could pull the cover on the traction battery while it is installed in the vehicle & run down the traction battery & then measure the modules. All 28 of the modules will track each other very well if they are good. The ones that drop the most contain failing cell(s)

One other thing...What I noticed on ScanGauge is that when I drive the car in EV mode or stay parked with AC on SOC from ~70% goes slow down to 50%.. When the car is under 50% it just deploys the battery to 35% in maybe less than a minute( not always tough, but most of the time) For example yesterday, till I got in to the tunnel the car was probably at 45% and then in the middle of the tunnel it was 25% when I saw that message...( NO AC ON)
ANSWER: I do have a ScanGauge. The SoC that appears on the dash of the Prius is NOT an accurate gauge when the traction battery is failing. With a _good_ traction battery installed, the dash gauge is fairly accurate, but very slow to respond. Note I have stated a few times before - the Prius tries _very_ hard to keep the battery at 60% SoC. With a failing traction battery going below 60%SoC is like falling off a cliff. There is just no more capacity in the failed cell when it gets somewhat discharged.

What I tried to do to keep using my traction battery for another few weeks/month(s) was to avoid getting the battery out of its 60% SoC area. If I was stuck in traffic or had to sit for any length of time I would keep the Prius in "D" with my foot on the brake & press on the accelerator to force charge the battery. I would try to get the battery back to 60-62% SoC then let the ICE shut down.
Also I would try not to use the AC if stuck in traffic as it pulls the batt. down fast (with a weak traction battery).
If I found myself having to slow down from speed lots, to keep the battery from getting much over 60% SoC I would turn the AC on high (very cold) to use up the regen. amp-hours that got put in the batt. Remember the Prius will set a code during regen braking also if one cell gets fully charged & its voltage soars.

Gosh, I'm tired now! Happy reading
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Well I really appreciate your time writing all this !!!

Now I understand what you are saying. I will try to track which module is the weakest in the next coming week and hopefully I will be able to narrow it down and order a new module...
Will replacing a bad module give the traction battery a good condition status for some time ?

And what do you think about a grid charging ? I asked the guys at Hybrid Automotive Restore you Hybrid Battery, Don't Replace it!, they will have availability for the gen3 in the next 7-8 weeks.

nedim · Feb 18, 2015

Alright, so I opened the cover and measured each of the 28 cells while SOC was 38%.
7.47 being the highest cells on each end of the battery and 7.40 being the lowest somewhere in the middle. The ones next to it are higher by 0.1 and it increases till the last ones to 7.47.
So do I blame that cell showing 4.70 for the fast drain I am experiencing or do I blame almost every cell?

The orange plastic tool shows which cell I am mesuaring .

kc410 · Feb 18, 2015

nedim said: ↑

Alright, so I opened the cover and measured each of the 28 cells while SOC was 38%.
7.47 being the highest cells on each end of the battery and 7.40 being the lowest somewhere in the middle. The ones next to it are higher by 0.1 and it increases till the last ones to 7.47.
So do I blame that cell showing 4.70 for the fast drain I am experiencing or do I blame almost every cell?
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A few problems pop-up:
1) Measuring battery voltage with no load is problematic - the cells tend to equalize their voltage rather fast.
2) With a very good battery all 14 of the module pairs stay within 0.1V for the full range they are operated at in the Prius (40-80% SoC).
Therefore all 28 of the individual battery modules will also track each other within 0.1V or less.

Your voltage readings are only showing a 0.07V range between the highest to lowest modules. No meaningful results can be made with the individual battery voltages so closely matched.

I guess the first step is to identify if you really have a bad module pair by monitoring all 14 voltages & see is you have one of the 14 that is falling lots lower than the other 13. At 60% SoC all 14 may track very well. It will be when the pack is very low (or high) that one of the 14 will start dropping lots faster than the rest. This is where Blk#max & Blk#min will help.

A traction battery that is starting to fail will show Vmax-Vmin = 0.3V.
This will increase as the weak cell(s) get weaker. A battery with Vmax-Vmin = 0.7V is going to be setting a code soon.
Be safe driving when you are trying to monitor Torque
If you can see 13 of the battery module pairs tracking very closely & just one falling 0.7V or more below the other 13, then you have identified two battery modules - this would be the very minimum start - after this it is just narrowing it down to one of the two modules.

Keep in mind these readings are under load (as the battery is discharging).
NOTE: again, when the battery SoC is in the normal range (60%) it is quite likely all 14 banks may be matched to within 0.1V.

Another problem that creeps in is ALL 28 modules are well used & it is likely there are 2-3-4 modules that are weak. Of course just the weakest will probably show up at first. Once the weakest is replaced, the next weakest will fail etc

More in the next day or so if needed - got to be up early

Former Member 68813 · Feb 19, 2015

nedim,
did you check if the bus needed cleaning while you had that opened?

It might be time for a new traction battery....

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It might be time for a new traction battery....

nedim Junior Member

nedim Junior Member

kc410 Active Member

Former Member 68813 Senior Member