GM Volt Forum banner

2012 Switches to gas mode with Battery Charge remaining

19511 Views 52 Replies 22 Participants Last post by  hellsop
I have a 2012 Chevy volt with 140,000 miles. It has not had any issues until now. The car will switch to gas mode while there is still plenty of charge remaining in the battery (as much as 80%). The temperature is well above freezing. Stopping, shutting of the car off and restarting resolves the issue. I took it to the dealer. however, the computer was not writing any errors codes.

Any ideas what could be causing this?
  • Like
Reactions: 1
1 - 2 of 53 Posts
I know you probably don't want to hear this Paul but you likely have a bad cell group in your battery. Just one. I had the exact same symptoms and the local Chevy dealer had the car plenty of time and never found the issue. There are no codes. The way I found it is to first buy a VCX Nano and get it running. It runs a Windows XP virtual machine (VM) on your laptop to allow the use of the factory GM GDS 2 software. After I got the GDS 2 working (It took me a while to wrap my brain around how the program was run on the VM), I was able to get in and scan the car's battery control module. When the car was hot off of the charger each of the 96 cell groups was at 4.07V per group, except one. There are 96 groups. The outlier cell group charged to 4.12v. Hmm, I thought. I set the laptop in the passenger floorboard and then drove the car till the battery was depleted. The weather was warm so the car ran on electricity the whole time, about 24 miles if I remember right. SO, at the bottom of charge, the cell groups were distributed around 3.60v with a variance of about .02v. The outlier cell group (number 2) that overcharged at the top end was down around 3.40v and falling fast! I knew then that my problem was that cell group number 2 was B-A-D. I finally had my answer. I took the car back to my local Chevy dealership to see if TAC saw any interest in my situation (I had 174K) but alas, no, they said I was on my own. The fact that the car showed no error codes with an obviously bad cell group I thought would interest them since they had reflashed my brand new Bolt EV for the Same Exact Thing so that it Would trip a code if there was one bad cell group. A safety issue. Hmm.

When I got confirmation that I was being kicked to the curb (I'm not sore), I decided to swap the battery myself. There's a thread stickied in this section about my swap.

I recommend that you get a VCX-Nano setup. If you don't want to do it or can't I can lend my setup to you. I am interested to see if you have the same thing going on. I think you do.
See less See more

I think that are in a good position to get a new battery or module under warranty in my opinion. I would always argue for a complete new battery. Anyways, I would take the car back to the dealership and tell them to look at all 96 battery cell groups at the time when the car is just finishing charging. They should all be around 4.07v, plus or minus .01 volt. They should make note of any cell group voltages above all of the other cell groups. Have them print out the voltages for every battery group at this state of charge. They should leave the computer hooked up and go drive or have a porter go drive the car very gently until all of the battery range remaining has been depleted. This means it shows zero range remaining on battery, not just when it kicks over to gas the first time. At that point look at the 96 cell groups again and see which one(s) are significantly below the average cell voltage. It should finish at around 3.55-3.6v per cell group. If there is a bad cell group or groups then there will be a low voltage cell group or groups and this will be enough to get TAC involved. Ask for a print out of Cell Group voltages at the top and bottom of charge. Do not accept no for an answer.

I would do this before either getting my VCX Nano setup or buying your own. They have to verify anything you find anyways so it will be likely cheaper and more time efficient to ask them to do the test first. Now, they may give you the runaround and say they did the test and they cannot give you a printout since their printer is broken, yada, yada, yada. If that happens you will have to get your own proof or find another dealer, assuming the test came back that cell group voltages were OK.
See less See more
1 - 2 of 53 Posts