Q: 4wd service light on, selector switch will not shift to 4hi, 4lo or neutral. on 2003 GMC Sierra 1500

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I have the "Service 4wd" light on, selector switch will not change from 2hi to neutral, 4hi, 4lo or Auto 4wd. Tried a new selector switch with no luck. Trying to decide what next to check?
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I hooked up my code reader to the OBDII port and didnt see any codes at all, the only thing showing was my Evap, O2 and Catalytic Monitors were INC but those are a different problem. Is there somewhere else to plug into? Thanks for the help/advice.
I dont hear anything trying to shift at all.
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