When the light isn't coming on, I can shift into 4wd high, put it in drive, go forward a bit, put in reverse and go back a bit, and the light still doesnt come on. I can goose the gas and see the front wheel spin if I'm on dirt and verify its in 4wd. I can do the same for 4wd low, and the gearing changes, but no 4wd light there either.
My understanding is that the 4wd light should come in blinking if 4wd has been enabled, and then go to solid when engaged. 4wd is engaged and the light is neither blinking nor solid on.
This problem is intermittent though. Sometimes the light comes on just fine. That's what has me sort of perplexed. If an ECU goes bad, I would expect it to fail all the time.
I'm just glad it was failing when I took it into the shop. "No problem found" would have been totally annoying.