Service 4wd light and difficult to engage 4hi

[Sean1977]

the "Service 4wd" is lit and I have trouble to engage 4hi for my 2000 Yukon XL 2500.  To engage, the trick is : in stationary, go reverse, neutral, and then select 4hi.  Similarly to go back to 2hi.  I don't seem to be able to switch to 4auto regardless.  Any idea of what is wrong?  Thanks!

[Formulabruce]

The dash control pad unit has cold solder joints and or a bad auto switch. Replace that switch assy. I would NOT get a used one.  Good luck !

[Sean1977]

It worked.  Thanks!