Ford’s recall of Mustang Mach-Es in 2022 is under investigation by feds
arstechnica.com
arstechnica.com
That said, like you said, if it overheats it's a contactor defect. They're either on or off and doesn't switch live loads. They shouldn't be using the same contactor in the GT as they use in the lower end models, purely because the GT has a much higher current draw under load.
Instead they probably screwed up something in the precharge or disconnection process.
The contactors should only open or close when zero current is flowing. However that's often hard to achieve. Specifically, things either side of the contactors often have smoothing capacitors in, and all those smoothing capacitors need to be charged to the exact same voltage as the battery to ensure there is no sudden large current as the contactors close. If that happened, even once or twice, the surface of the metal contacts becomes non-flat, and then the contactor will have a higher resistance and overheat.
There is the same problem when opening the contactors. No current must be flowing, but sometimes that's hard to achieve when there are lots of things connected to the high voltage bus, and any one of them might be drawing or supplying current. It isn't helped by the fact that opening the contactors will probably be done in most fault conditions - and fault conditions could easily have large currents flowing.
They're basically a big battery switch that disconnects when the car is parked or if a fault occurs.
However, in the fault case, pyro disconnects can be used (explosively cutting the wires). They're far cheaper.
For the 'parked' case, MOSFETs inside motor inverters have low enough leakage current that there isn't a need to power them down.
The only remaining time it's useful to have the contactors disconnected is when doing maintenance on the high voltage system (motors, AC compressor). That's a rare enough event that I would think the technician could just remove some bolts to physically disconnect a wire for maintenance.
A switch that never switches is just a waste of weight, money, space, resources, etc.
Still, kudos to Ford for building electric vehicles for their core truck and sports car markets. I wish them well even if I don't trust them enough to buy their product thanks to doing things like this all the way back to the Ford Pinto and most recently with the 2022 Mustang Mach-E.
The only “software fixes” for the issue was logic to preemptively detect an impending failure so people wouldn’t get caught on the side of the road.