Sounds exactly like what I stared experiencing after I had an oil change done on my truck. Low oil pressure warning started about a week after the oil change, the first time I was between the garage that did the oil change and the dealer where I bought the truck. Went back to the garage, checked the oil, it was full, they weren’t really sure what the cause could be, stopped at the dealer, they looked it over and could find any obvious signs of leaks, but since it wasn’t OEM oil they wanted to start there.
Had the dealer do another oil change a week later, took a drive that afternoon and still had the low pressure warning. Went back, the service advisor was able to witness the warning, went it to get the shop foreman, and by the time he came out and plugged in the warning wouldn’t come back. Scheduled to replace the pressure switch/sensor, job completed, took a drive when I got home te same day, warning came back.
By now I had noticed that it happens when at operating temp, in gear at idle. Mad another appointment for them to have the truck a few days so they can drive it and do a live feed scan.
Got a call from the service advisor today saying that Ford released a TSB a day ago covering this issue, he’s ordering the part to hopefully have it on hand next week when they have my truck. Unfortunately, it doesn’t look like Diesel engine or extended warranties will cover it, but he’s going to try and get them to eat some of the cost. He has the same engine in his truck and hasn’t experienced this issue, nor have any other trucks they service.
If they determine this is the cause, is replacing the spring and Nub difficult to do?