[saghost]

The actual state of charge of a Lithium battery can't be directly measured by any instrument developed to date. The cars use a math model based on the voltage and tracking current in and out to calculate the SoC.

It's always been normal for it to adjust up or down a few miles when the car is parked - as the actual resting voltage of the pack can be measured and used to update the model (when the car is on, power flow to/from the pack causes voltage to bounce around.)

What you're describing isn't normal, though. It sounds like the math model is getting some conflicting inputs, resulting in unpredictable behavior. MY guess is there either a failed sensor or a loose connection or cells going bad, but I'm not nearly enough of an expert to tell you exactly which, and I haven't read of this exact issue before.

 

[jbakerjonathan]

I agree with Walter. I think that it is a faulty sensor that allows different voltages to be reported in an almost instantaneous fashion, causing the algorithm to develop wildly different results. The sensors are probably mounted on the battery. Any repairs would probably require the battery to be removed from the car. That is my WAG. Good luck.

 

[bentbiker]

Have you replaced the original 12V battery? Weird stuff happens when that battery starts to fail.

 

[GlobalTexan]

Thanks Walter, Jonathan, and Bentbiker for your helpful suggestions. Sounds like first (and easiest) to check is the 12V battery (never replaced, never given me a reason to), and then back to a dealership for testing of battery sensors...They may be reluctant to do so, since I know it's an involved process to remove the battery pack - and there's no code faults shown. I'm thinking I may need to get GM on the phone to see if they will support.

Warmest (and I mean 105 degree) thanks to all.

 

[AlomostEV]

I literally have the exact same thing happening to my 2013. It has been happening for the past year now and has been getting progressively worse with more and more random PPR messages as well as the switching back and forth between ICE and EV operation even though range is remaining. I have taken into my Chevrolet dealership many times and even demonstrated the PPR message just sitting in their service drive. But after consulting with GM TAC they tell me there is a cell or multiple cells within my battery that are becoming weak but until a fault is stored there is nothing they will do for me. It has been frustrating to say the least.


To answer your original question, you have failing cells and need a new HV battery pack.

 

[GlobalTexan]

Thanks again, AlomostEV - all your answers seem to point to the same general area - either batteries getting worse, or the sensors giving the impression of problems. Then not. Then again... Yes, it's been a bit frustrating, but I'm hopeful I can get this noted on a file somewhere at GM, so that even if it fails 20 miles after the warranty runs out, that the case can be made that this is thoroughly documented as being a present problem while still under warranty.

We'll see how serious GM is about customer satisfaction versus simply trying to avoid responsibility. I wonder if leadership was part of that group that signed up on the new Business Roundtable statement about corporate responsibility?

 

[eDreamin']

To answer your original question, you have failing cells and need a new HV battery pack.

More accurately, you'll probably get a new module, not the whole pack, once the computer can pinpoint the bad cell(s). I would be frustrated, too. Maybe take a picture of the next reduced propulsion message and take that to the dealer?

 

[Jiminy]

I had similar issues with my daughter's 174k 2011 Volt. You can read about it here:

https://gm-volt.com/forum/showthread.php?321946-A-guide-to-swapping-your-Gen-1-Volt-battery-at-home

Jim

 

[GlobalTexan]

Jiminy,

Fascinating - best description yet, both of the symptoms I'm experiencing, and a possible/likely way that I can tip the dealer's hand on what to look for. If I'm nice/tough enough, I will be working towards asking them to show me the exact same cell tests/measurements that you did. If it's a bad/weak cell - even if its not throwing a code - it looks like it should show up. Thanks for the deep dive, and very useful insights!
Scott

 

[Jiminy]

Hi Scott,

I helped another guy here get a battery replaced right at the 100k mark by using the top/bottom method. The dealer was telling him the same thing that they couldn't see anything concrete wrong and his warranty was expiring so he had to school them on the method and he finally got what he deserved.

I did a buyer's check for a fellow forum member today on a 165k 2011 Volt and at the bottom of charge all of the 96 cell groups were very tightly grouped together which made me think that when I charged the battery fully that I would see the same, a well balanced pack with no outliers. Well, I charged that sucker up and hot off the charger got this result:

I was very surprised. Cell group 4 and 8 show the classic failure mode. My theory is that one of the three battery pouches in cell groups 4 and 8 were bad which reduces the capacity of those cell groups. The reduced capacity allows those groups to overcharge up to 4.11v and 4.12v just like on my daughter's Volt's original 174k pack. Needless to say, I am glad that I took the extra time to charge it up fully to check this. I'm pretty sold on this method for any buyer's check now.

 

[GlobalTexan]

Hello again, Volt-ies (Voltoids?);

Just beginning to realize that I've been living on borrowed time with the original 12V auxiliary battery... I've sourced a Group 47 replacement, and it's on the way... Now, I looked elsewhere in this forum about how to change the battery, and the step-by-step that I found here:

https://gm-volt.com/forum/showthrea...ement-FAQ&highlight=OEM+Part+Number,+88864083 )

Doesn't seem to suggest the need for an OBD2 battery saver while changing the battery. Does that make sense to you? I was assuming that I'd need to ensure continuous power to the computers - if only to avoid scrambling it's brains

 

[Jiminy]

I've changed 12V batteries four times on three different cars. I had to disconnect the 12v on my daughter's car when I swapped the HV battery, too. The car won't care if you disconnect the battery terminals. I do suggest putting the battery on an automatic 2A charger if possible to charge it fully before using it. -Jim

 

[JuneBug]

I replaced my original Delco battery with the Duracell from Sam's Club back in June. After re-connecting the cables the only effects were the compass and TPMS displays showed dashes. After starting up and driving a bit, everything went back to normal. Didn't even affect my radio presets.

 

[GlobalTexan]

Thanks Jiminy & JuneBug! Gives me some comfort that this will be easy to do!

 

[JuneBug]

Thanks Jiminy & JuneBug! Gives me some comfort that this will be easy to do!

You need a small ratchet with deep 10mm and 13mm sockets, plus a short extension is helpful.