The software update, as the letter implies, will not correct the problem. The WOT sensor substitution will do so.Sorry if this has been rehashed already, I promise I read through 5-6 pages at the front end and 4-5 pages at the back end of this thread. I rec'd a letter from GM yesterday that my '14 needs the sw update to increase the warning time before it goes into limp mode (HPCM2 issue). From what I've gathered it's mostly '13's impacted (my '14 was bought in Dec '13). I don't have time or desire to mess with buying and installing the inline harness bypass and messing w/ the fw update on the ACDelco site. Should I have the dealer perform this work? I haven't seen a lot about people getting these letters in the last few weeks and how it's related to this thread or not. Thanks for any advice, all you guys are so much more knowledgeable about this car than me!
Edit: If it helps, the number at the bottom of my letter (simply dated "June 2019") is: N172130462 (18217)
What the software change does do is extend the time between the sensing of low coolant in the battery cooling system and the reduction of the power, giving you some precious time to pull over out of harms way before power is shut down. The desire of the engineers was to protect the battery. They inadvertently caused potential peril to the occupants of the Volt due to the short timing sequence in the original software.
The problem can occur in all the Gen1 model years, including 2011 and 2012 having had the battery mod performed by the dealer.
If you want to remove any possibility of having an erroneous low power event from occurring, I recommend that you install the WOT sensor. As was explained by WOT (somewhere on this list <grins>), there are other sensors that will protect the battery in the event of coolant loss or low level. The current wisdom is that the additional sensor added to the mod was for political reasons made to insure that the government entities would be satisfied that the problem(?...there are two schools of thought on that) had been sufficiently dealt with and GM could get on with selling the Volts.
The substitution is NOT that hard to do. The instructions are easy to follow. I wrote of my experience in doing so (somewhere on this list <grins>).
EDIT: OK, I looked up my posting. It is #192 dated 4/18/2019