Hello all - I'm hoping you can advise, as I have a similar issue.
I had issues last winter with my 2017 Cmax Energi. It ran fine on the electric engine, but seemed to have trouble switching to the gas engine for passing, or when the electric charge ran out. It also chugged a bit when on the gas engine and I turned the key to shut off the car. It was worse in cold weather. I got the wrench light and took it to a mechanic who drove it around a bunch and couldn't get the light to come back on. So, I kept driving it, and noticed it still had a lag in getting the usual oomph when trying to pass, but otherwise charged and drove well. This winter, the probaly started early, when temps really weren't that cold (by Montana standards). The same issue with switching to the gas engine and chugging when turned off. The wrench light came on, then the engine light, and that stayed on. I took it to the dealership and they tell me I need a new high-voltage electric battery, to the tune of almost $8K. There is 108,000 miles on it, so I'm told it's out of warranty for the EV system. Any advice? Is it worth taking it somewhere for a second opinion (there aren't many mechanics here that work on EVs.)? I don't know if the car is even worth that. It seems the issue is switching to the gas engine, so could it be a different problem?