I am assuming you have the dial on the dash (electric shift) like in the photo below?

 

Can you describe your procedure for shifting into 4x4? Do you have stick or auto trans? Do any lights illuminate on the dash for 4x4? Do you hear any solenoid engagement at the transfer case?

Read Post #2 by RustyGold for a full troubleshooting procedure:

https://www.thedieselstop.com/forums/f24/my-own-7-3l-won-t-start-644185/#/topics/606841?page=1

 

Yes I have the control on the dash.
The truck is a auto trans I have disconnected and blocked the auto hubs. the 4x4 light on the dash flashes on when the key is turned on then goes out.
I here nothing from the solinoids or the shift contrlo motor in the transfer case.

 

Can you check for DTC Codes?

 

I just checked and the only coce I got was po603

 

I just checked and the only coce I got was po603