If it was the CHECK OIL LEVEL message and you had the oil changed, he may not have put enough oil in it. The Northstar takes 7.5 qts. (most cars hold 4-5 qts).
The message comes on when you are about 2 qts low.
Check your dipstick. The proper oil level should be about midway in the hash marked area.
if you don't have an owner's manual, check the sticky at the top of this page. Free downloads.
Definitely check the level yourself. Many oil change guys assume 4-5 quarts is full. Our Northstars take 7.5 with filter. I start with 7, check and add as needed so as not to overfill. I've never had the check oil level light come on .
Two "oil" warning messages - "Check oil level" means about 2 quarts low. "Low oil pressure - stop engine" means just that - less than 5 psi. Maybe the sending switch. (Both parts from Rock Auto)
7.5 quarts to the middle of the dipstick hashmark is full.
The oil level sensor sticks out the left (front) side of the oil pan, just below and left of the oil filter and filter adapter. You need to drain the oil to remove and change it. Maybe just the wiring/connector.