I have a 2020 Chevrolet 2500HD. I am getting a warning on the dash to Service 4wd. The pickup runs in 2HI, it will not switch to 4HI or 4LO. The problem is, the check engine light is not on, and there are no codes stored. I ran an OBDII code reader on the pickup to try and figure out what is causing the Service 4wd warning, but to no avail(no codes). What are the possible fixes for the Service 4wd error?