New to this forum so I'm hope I'm posting this in the right spot I have a 1999 Buick LeSabre with 80000 miles on it when you're going down the highway the engine will just shut off just like you turn the key, however if you put it in neutral while coasting and hit the switch and I'll start back up and run fine. It's been doing this for about a month with no Rhyme or Reason as to when it might shut off use the car last weekend for 8 hours with no problems. Wife used it yesterday and it shut off twice for her I used it three times today with no problems. No codes showing. Looking for any suggestions as to what the problem could be. I don't believe it's a fuel issue because it starts right up but I am open to any suggestions thanks for your time I'm hoping one of you text will have an idea where to begin as I checked the battery terminals and the voltage on the battery is at 13.3 so I'm assuming it's not battery-related

 

Sounds again like the crankshaft position sensor or maybe those have the camshaft sensors also. They seem to crack or moisture permeates them and nothing is for certain after that. Used to have the exact same issue with the Chrysler pointless distributors.

The dealerships can't seem to locate that particular issue either unless the CPS remains bad. Will check them and nothing appears defective. Relearn may have to be performed, can't say about a '99.