transmission wont engage 4 hi light just flashes and service 4x4 comes on. on 2000 Chevrolet Silverado 2500

worked fine when i shut it off.

Asked by for the 2000 Chevrolet Silverado 2500
scan trans codes and post so we can adv
1 more answer
Sounds like your transmission controler is sensing a problem thus not allowing it to shift. Seek a shop that can scan powertrain system for fault codes and diagnose the problem.