All of the rest of the cell groups were more or less the same voltage both fully charged and with a depleted pack. Pretty clear to me that the battery pack was compromised by one bad cell group. If you let the car sit with no range left, cell group 2 just sinks further and further. The difference between high and low readings is 4C so I guessed that it still *could* be the issue. Below is a GDS2 screenshot showing the temp sensors. So I bought a VCX NANO setup and installed it onto an old laptop running Windows 7. The most important thing I learned from the first visit to the dealer is that if I was going to have a chance to fix this car I was gonna have to get my hands on a GDS2 setup. Not one seller could do that for me as the sensors are buried in the module and can only be accessed by destructive means. I got on ebay and looked at all of the Volt modules for sale and asked several sellers if they could locate a temp sensor in a used pack and sell me one. They were all the same (at that higher state of charge) which led me to think it must be a bad temp sensor alone causing this issue. When the car was at the dealer they let me look at the screen in GDS2 showing the voltages of the individual cell groups. The first thing I thought was wrong was that the pack had a bad temp sensor which was forcing the ICE ON to protect the battery. If I had left the P0C36 code in there they would have had something to start a dialogue with TAC with. When they couldn't find anything concrete they did the triple honk update and replaced my hatch struts for free and said they could do nothing about the issue of uncommanded ICE running since there were no codes present. They had never worked on a car with such high mileage and were a little lost in diagnosing an issue that presented no codes. I dropped the car off at my local dealer to see if they could figure it out. It was the original battery! Needless to say, putting a GM battery back in seemed like a no brainer. I was shocked to find a date code on the original battery that said 2010. As I mentioned before, I replaced the 12V battery to preclude that causing any issues of its own. On one cold (40F) morning it started the ICE as soon as I started it and ran for a few minutes and then switched back to EV mode. It would run a few miles in EV mode and if there were any rises in the road it would switch back to gasoline so it seemed load dependent. It would run the gas motor for 2-4 miles and then switch back to EV mode. The weather was coldish (for south Texas) and so what it would do was run for about 24 miles on electricity alone and then switch over to gasoline with 8-10 miles left of AER. Well I got the car home and immediately started trying to figure out what was going on with it.

That said, I wouldn't do it differently if I could though. Long story short I ended up buying the car for $3800 which I thought was a pretty good deal. I replaced the 12v battery with a new OE battery shortly after buying the car. I used to see all kinds of electrical anomalies with cars that sat around with weak 12v batteries. The car sat for a couple of months before the previous owner decided to sell it and I think it was just a spurious code generated by a tired 12v battery. My opinion on that code is that it was generated by the low resting voltage of a 7 year old OE 12v battery. This was a mistake in hindsight as the local dealer couldn't start a ticket with Chevrolet without a current fault code stored in the hybrid system. I cleared the code and it never came back. This means that the sensor saw full cold at one point or that it was an open circuit. I did have the Torque app and I scanned it and got a P0C36 code which is a cold temp sensor 6 issue. I should have known right then that I was barking up the wrong tree. I asked the owner about that and he said sometimes the ICE would run before the HV battery was depleted. When I first test drove the Volt it only had a few miles of range left yet it had been running on gasoline. I am very experienced in messing around with cars so I didn't think I was getting myself into something I couldn't get back out of. I knew it was a risk to buy a car with so many miles but this would be my third Volt and the general consensus was that Volt batteries just don't go bad.

My car is a 2011 Chevy Volt that had roughly 174,000 miles on it when I bought it in February, 2018.

2013 chevy volt battery replacement