disconnect the 2 plugs for about 30 seconds (module have tendency of locking up)
IMPORTANT... look at the plugs for signs of corrosion (very common)
if OK, then plug them back in and try to Switch to 4 hi.
If OK, no further action needed.
If not, then the system needs to be diagnosed, the module stores the failed code, and a scanner is a must. - Another thing to try is to reset the TCM ( transfer case control module). Disconnect the ATC fuse in the under hood fuse block for 1 minute to clear the codes. Cycle the ingnition key on and off 5 times. Reinstall the fuse. Recheck 4x4 operation.
There is a electric motor on the t-case called an encoder motor this motor gets stuck when shifting out of 4lo to get it out let the truck roll forward slowly with the wheels straight this will allow the encoder to come out of 4lo. Common complaint on these trucks but in some cases motor needs replacement.
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In some cases reset helps, to reset unhook the battery for half an hour then hook it back up and try it.
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If again n again your truck goes to 4low then its either motor issue or the TCCM issue.Transfer Case Control Module.The wire from motor connects to TCCM.
