2008 Mercury Mariner Hybrid

Usually on the highway, my vehicle will show the warning light (Master vehicle electrical hazard warning lamp) with the message “Stop Safely Now” and will power down and I have to pull over. So I pull over, turn off the power, and sit for a couple of minutes, and then start it up again and go a little bit farther till it happens again. Sometimes it might only do it a couple of times and other times it may do it 15 times until I can get it home. My husband had an R&R sensor replaced at a Ford dealership awhile back and we thought that it had fixed the problem. I have driven it on a trip of 1500 miles and it never once gave me this problem, but recently it has started to act up again and I am hesitant to get it back out on the highway. Any ideas?