2000 Blazer Won't Go Into 4H

Hi All:
The vehicle in question is a 2000 Blazer with 81,000. It will go into 4 Low with no problems but will not go into 4 High all of a sudden. This is
something that just started today. Don't know if all of the 2000's are electronic transfer cases or not, but this one is.
The owner's manual says to put the truck into Park while the 4H light is flashing if this happens, but that results in nothing. Both the 4H and the 4L lights flash when 4H is selected. If you select 4L, both lights flash briefly and then 4L engages. If you select 4H, both flash briefly and then 2 comes on.
Tried shutting the truck off completely - no luck.
Any suggestions appreciated.
--

-Mike-
snipped-for-privacy@alltel.net
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I had a similiar but not exactly the same problem with my 99 Sierra. Mechanic replaced what he called the 4x4 switch which is located in a vulnerable position near the front axle.

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