[...] So yes, it's possible to drive on one motor. Sometimes.
I can confirm it's possible, at least in some cases like mine, to continue driving on the front motor only after the rear drive unit fails.
This happened to me on Monday as well. P85D.
I got the rear motor disabled message. I was able to continue to get off the freeway using the front motor I assume.
Once I got off the freeway and put it in park...I could not move at all.
Flatbed to the shop...48 hours later and and new Drive Unit, she was just delivered back to me.
Mine was an almost identical experience as
@jsimon77, with my 70D three weeks ago,
as I described elsewhere
only difference, after seeing the dash warning I continued driving a few blocks on front motor only, then pulled over and put the car into Park. Without getting out of the car, I put it back into Drive (rear motor warning still there), and I then was lucikly able to drive the remaining few blocks home.
But next day I wasn't able to put the car into drive again (I assume, after the car powered down overnight the system disabled the front motor to be safe?). Flatbed, loaner car... etc... 2 business days later got the car back with a new rear drive unit. Annoying but at least it was near home when it failed and I never had to set foot in the Service Centre myself nor be without a car.
p.s. here's a Tip:
if this ever happens to you
don't park the car nose-in into your garage before calling service, like I did. I had assumed I could continue to drive on the front motor alone the next day so I didn't think to leave the car out on the street (bad move)
It was very hard to push my car backwards out of my very narrow garage and up the almost imperceptible incline of my driveway, before they could tow it up onto the flatbed. Of course, the only tow hook on this very heavy car is at the front... The SC had to send a couple extra guys to my house to help push, after the flatbed driver and I only got it out halfway.
