if you have a programmer for your truck you should be able to read it with that, other wise most auto parts stores have a scanner you could rent...otherwise a dealer can. but if your transfer case still works fine and everything seems ok im more than certain about that switch. have replaced 3 in the 9 chev's i own. its a simple fix.
When mine went out on my last truck, I noticed that I had to push the switch a little harder or push it a few times to get it to work. Shortly after, I got the light. My dealer had one on the shelf-I guess it's common.
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