Same thing happened to me. It is easy to trouble shoot but the a new 4wd air pump is around 400.00 bucks or more. 1st find the pump. its located just behind the front bumper just right of center it has a small wire harness and 2 black air tubes connected to it. disconnect the harness then start the car if the light is on then the pump is bad and i can help. do not buya new one because GM charges too much. I also thought it was just a indication problem but it was not. if it can shift in andout no problem wrong when you shift in to 4 hi or lo there is an air pump that comes on to engage the front axle if that does not happen you are not in 4wd all that happened was you are sending torque foward to the front axle and you can feel a slight differance in how it drives but like i stated the front end is not engaged. the light will not come on untill the pump has come on and built up pressure to turn the light on with a pressure switch in the pump.
trackerfixxer
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