I have seen articles which may leave that impression with some readers as well.

This is a new “recall” or service campaign that covers the same underlying problem but it makes additional fixes that were not part of the earlier update targeted at 2017 Bolt EVs. It has a new “GM Recall” number of 18125 whereas the previous one was 18097. Thus it is confusing to simply frame it has an extension of the earlier fix to new cars (the 2018 cars).

All 2017 Bolt EVs and essentially all 2018 Bolt EVs are recommended to be taken to a dealer that can apply this new update. For 2018 Bolts, it is the first time they are getting the aspects of the fix that were part of 18097 that give the driver more time and notification due to an imminent need to reduce propulsion power and get off of the freeway etc. I’m not sure if any recently built 2018 Bolt EVs have received the new software at the factory already so it’s possible that some 2018 Bolts don’t actually need to be updated. It does seem clear that most or almost all 2018 Bolts need to be updated.

In addition, the 18125 GM Recall update improves the GOM or Guess-O-Meter range estimation behavior so that it better reflects the actual range of the car due to one of the battery cells (cell groups) being less able to hold and release energy due to the cell having a manufacturing defect. Although the GM spokesman I talked to didn’t want to get into the details of the new GOM behavior, I believe what this means is that the GOM now estimates the range based on the weak cell’s voltage and stored energy estimate whereas in the past it was using some kind of averaging across all of the cell groups. Since the weak cell group (with 1 of its 3 cells going bad) is capable of holding less energy it will run out sooner while the other cell groups still have energy. The car must stop withdrawing energy from the battery pack when the weak cell group is empty because continuing to drain it will cause further damage to the cell group and perhaps physically damage it. The 18125 update may also include a small number of other changes or improvements that are not directly noticeable by customers.

With this new GOM update, the car should no longer suddenly show a big drop in estimated driving range when the reduced propulsion warning is given imminently before vehicle powertrain shutdown.

My information comes from a detailed telephone discussion with a GM press representative.