OK so here's my story. 2013 fusion 41k Miles. We flat tow behind our motorhome to Burlington VT. Nice place mountains fall colors blah blah. We run the car all week and on the last night before we leave we go up the mountain through smugglers notch and then up the toll road in Stowe resort to the top of the mountain. 4700+ feet. The toll road was supposed to be 4.5 miles long. {Right after we got our car in aug 2014 we took it to NH and we up Mt.Washington x2. (9 mile roadstraight up)} so I figured this would be no big deal. 3/4 of the way up the mountain we get a wrench light... I figure the car is getting hot, the engine/ transmission working hard to pull us up the mountain, once we stop at the top, let it cool down it will be all ok. 2.5 hrs later we come back to the car get in and nothing! Everything came on except the green arrow to drive. Got the stop safely now screen. the check engine light was on, spanner wrench and red triangle of death. 6 hours later a tow truck pulls us off the mountain back down the goat path in the dark.(Thanks and shout out to security at Stowe resort to save us until the tow truck came.) So car is towed to Heritage Ford in Burlington VT b/c they have "service hours" on Saturday, the day were supposed to drive home. Well ends up we leave the car in VT and drive home b/c I dont know if flat towing back home will do damage to the transmission since I cant run the engine every 6 hours to reset electronics and some oil over the gears. 3 business days later they finally diagnose the issue as a failed HVB cooler??? Thank god for extended warranty! So is this the TCU issue also? I was there while they checked the 12v battery and it charged and tested fine. It was drained but checked OK on their machine. I'll work on getting the ECU codes. So some things that I've noticed prior to the failure. Very frequently the car will trip our lvl2 charger as fault. After awhile it automatically resets and charges. I figure this is all a battery temp issue and won't charge till the battery is x degrees and can accept additional heat from charging. I've always heard the cooling fans kick on when it does charge. So questions: Does driving up and down steep hills in low gear at low speeds strain the system too much? Would using hill assist in "D" be better? Doing both "L" and hill assist? Does anyone else "smell a hot engine" if it's been working hard cause we get this every now and again...especially in the above situations. I'll update as I'm told more. I think this is a big fail in design. If the EV system is faulting out why wouldn't just decouple and allow the ICE to run all the time. That would have at least allowed us to drive down the mountain ourselves and back home where I am slightly more comfortable with the service guys I know and not a shop 600 miles away :/