SERV 4WD light came on and I have a clunk in the front end when turning....

What causes the SERV 4WD light to come on?

the light under 2WD on my dash is blinking at me. (i have the electronic transfer case) What is causing this?

 

Encoder motor issue`s. It could be stuck halfway between 4WD engagement and 2WD.
Be careful, you could damage your transfer case if it`s stuck in 4WD.

 

It hasn't been in 4WD in a while....long while. over a 1000 miles....

 

The 4x4 actuator controler has an error/improper signal from the 4x4 actuator.
Take it to someone and see if they can pull a code.
I`m not sure if the 3 key cycle will work for 4x4 codes, but you could try it.
Cycle the key from off to on three times and see what comes up on the display.

 

Light came on and I shut the truck off...checked codes with a Smarty...overboost and PO602 both of which i knew about...i have to drive a while before the light comes back on...after I park it, its like it is erased. Now that i'm at the house, the light won't come on unless I go drive it a while...I'll play tommorrow. Thanks for your help.

 

Sorry. I had to edit my info. I was talking about a GM setup in my fist post . I don`t remember if the controller is capable of self diag.
I do remember something about dirty contacts. You might try some contact cleaner inside the switch and see if that helps.