4 x 4 High and low lights flash on and off on the instrument panel

What is your question?

When I was driving yesterday my 4x4 High and 4x4 Low lights started to flash on the instrument panel. They flash a few times and then go off and later flash a few times and this continued all day. I also noticed my gas mileage seems to have decreased. I took it into the dealership today and they said the test 4x4 module needs to be fixed for $595. What I would like to know is if this could be related to my gas mileage issue and also if this just means that I can't drive it in 4x4 mode. I hate to spend nearly $600 if it just means I can't drive in 4x4 mode. Thanks for your help.