I have a 04 Chevrolet Avalanche truck and the dash keep saying service 4 wheel drive.. Is it dangerous to continue driving it??

the worst that can happen is you blow your tranny, tranfer case or differential. check the fluid level. make sure it's where it should be. sometimes the selonoid gets stuck , turn it on & off and see if the light goes off.

My 2004 Avalanche did the same thing. Took it to an independent mechanic and he found that the steel gears would get just a little play inside the transfer case housing and ware a pinhole in the metal housing. The fluid had drained out of the transfer case and the transfer case had to be replaced. The new transfer case has a sacrificial bushing in it that protects against the same thing happening. About a $2200 fix but it works like new now.

Likely the sensor happened to me no you can drive it but you will not be able to use the 4x4 I have 3 not working one's really high and need's a shop to be fixed or the tool's auto part store said go to a Junkyard and get the two sensor's the other a shop.