03 envoy all wheel drive not engaging

Please forgive the long post but I am at a loss -

I have read the threads on here pertaining to the 4 wheel drive problems associated with the 4 wheel drive not working on the envoys. Here is my problem but not sure if it is an internal transmission problem, transfer case problem etc.. I purchased this vehicle for the 4 wheel drive capabilities.
We had a big snow last month, 2 - 3 feet for a week, The four wheel drive worked flawlessly.
The snow melted away but another little storm came in, I put it in 4 wheel drive but did not know it was not engaged as the 4 wheel light switched over from 2 hi to 4 hi. I realized it when I was sliding all over.
It did not engage the front wheels. I put it on jack stands the following weekend and had my wife turn the switch as I was underneath listening to the "Solenoids and switch boxes" do not know the correct terminology. It acted like everything was moving and clicking.
But I would spin the front wheel and it would just click as it turned. Not engaged into 4 wheel drive but showed it was engaged on the switch. I have read the numerous tips about the problem and the consensus is Vacumn or solenoid problem, Probably not an internal broken transmission thing.
What are the steps I need to take to see If I can fix the problem before I take it in to the dealer and have to pay 1000 dollars to change a fuse or something.
I am mechanically fit to fix most problems if I have a chiltons but this is my first ever 4 wheel drive and it has come along way from locking hubs.:frown:

I appreciate any help on this,

Jeff

Welcome to AF. I don''t know why the continued fear of having a dealer repair a vehicle as I spent 20 years in a GM dealership as SM and did not have any issues with overcharges. Anyway there are known problelms with the transfer case encoder, and the dash switch. This is a complex system and it it just not a simple issue of a vacuum hose or such. Is the driveshaft ( ft.) turning when in 4wd, if not the transfer case engagement is an issue.

Maxwedge - thanks for the reply - When the switch is turned, it goes through the blinking routine, then stops to state that it is in Auto or 4 Hi or 4 Lo, which ever I put it on. But when it is on the stand, I can spin the tire freely, In 4 hi, 4 lo it spins freely by hand but has a light clicking sound, I switch it back to 2 hi and when the blinking stops and is a solid light, I spin the tire again by hand and it is free but without the clicking sound.
I can lay underneath and have my wife turn the switch, I hear the little black box units moving and engaging but they sound really rough.WHen the stop moving. I turn the tire and again no engaging of any gears. Tire spins freely but clicks. Oh and only one front tire is off the ground.

I hope that makes sense

Is this unit a Vacumm, magnetic or electric solenoid mechanism as all of the weekend mechanics I know all say something different. It will probably be taken to the dealers to fix but I just want to make sure it is'nt a fuse or switch or vacumm thing before hand as I cannot afford a new front end or transmission.

Thankyou for the assistance,
Jeff

Most likely the encoder or the transfer case itself, by your description.

Is this unit a Vacumm, magnetic or electric solenoid mechanism as all of the weekend mechanics I know all say something different.

The 4WD system on this truck is completely electronically controlled. Like maxwedge mentioned, the encoder motor/sensor is primary control at the transfer case. No vacuum is used on this system.