Bdock1981

I have a 2018 GMC Sierra 3500. I keep getting the crank no start with code P129f. I have an Autel scanner and it says that it stores a permanent code of p129f. I let it set for 5 minutes or 3 days sometimes before it will start. Funny part is, after it restarts the engine light goes out. Took it to the dealership twice for this problem and they “say” that code shows no where in the history. What should I do????