I am midstream getting a pretty strange PHEV issue addressed, so I thought I'd start a thread with what has happened so far and update it extemporaneously, since these sorts of threads often help people later. Also, maybe someone here has seen something similar.
CONTEXT FIRST: This is a 2017 PHEV with about 45k miles, and I've posted a few other threads here before about battery issues I've had. Short version of those: Battery capacity has been degrading faster than it should, was around 72% last I looked, and 70% of spec is the "magic" line where Kia replaces the pack under warranty (10 years). Also have had issues on and off with getting warnings of "System Temperature High, switching to HEV mode" or the like.
The system temperature warnings have become more regular, especially on longer drives. But something totally new happened Saturday: I am maybe a mile into a drive from home, come to a light, press the brakes to slow just like normal. Then a few things happen all at once. The brake pedal seems to suddenly give under my foot, like the brakes had failed - but only for a fraction of a second, then the resistance came back. At the same time of the brake thing, I get a bunch of warning lights on the dash, and a pop-up that says I need to stop the car, turn off the engine, and check the hybrid system. Yikes. So I slow down to a stop at the light, in a left turn lane into a parking lot. Light turns, I go to hit the gas and pull into the lot, and realize the car is dead. Engine shut itself off apparently. Restarted the car (took two or three tries on the button), started OK but still had the check engine light on. Pulled into the lot and parked it up kept the car on.
Fortunately, I have an ODB Link device (I got it mostly for the PHEV Watchdog for the battery capacity issue). So I plugged that in and code the codes out. The car had thrown an error P0DE7. When I clicked on that error to get the detail, it says that it is a PowerTrain issue, and the ECU was "BECM-B+EnergyCtrl ($7E4)". When I look up the P0DE7 error, it must be quite an unusual occurrence because there were maybe 2 or three citations of it anywhere I could see on Google. It means High Voltage detected from HEV battery module (or cell). When I search that BECM thing, I get zero exact hits, but if I break it up I get info that it is about the battery control unit. The high voltage thing seems really strange, since the battery issues I have had so far are about the battery not having enough energy capability. Not the other way around!
So I drove it back home, check engine light still on. Yesterday (Monday) I drove it up to the dealer (Liberty Kia). Sadly the check engine light was off. But on the way up there (maybe a 15 mile drive) I got that recurring "High System Temperature" warning yet again. So I pulled it into the bay, kept it on, and watched them download all the various codes.
With battery capacity dropped way more than it should, repeated heat warnings, loud fan sounds from the back, and now this new issue, clearly there is a substantial problem with the EV aspects of the car. Shop sent the data and info to Kia, who came back today and asked them to do a "flight test", which apparently involves turning everything electrical in the car on at once and run the wheels in EV mode too, to see what the system does at stress. I was also told by the mechanic that it seems like Kia was leaning towards replacing the battery pack. I am pretty sure we were headed this way soon anyway (one more Chicago winter likely would have done it), but now it isn't just a battery capacity issue.
Because this is a warranty thing on the EV system, if they do indeed need to replace the pack, they cannot release the car back to me until they do. And Kia dealers don't just keep these packs lying around - they have to be ordered. So it seems I might be down a car for a while!
I'll update here when I get more info etc. Feel free to comment if you have any input, advise, questions, whatever.