4WD will not engage

As some saw from the non-T2S trip to Big Bear this past weekend, my 4WD (hi or lo) will not engage. I turn the switch to 4hi, dash light flashes at the normal interval, then speeds up to a quick flash after 10 seconds and stays that way until I turn it back to 2WD. No mechanical engagement noises of any kind. I've tried switching in neutral, park, rolling up or down hill, pulling the battery cable, tapping the front diff and actuator with a small hammer, and an OBDII scan with no codes showing. No luck.
As much as I like driving like Ken Block in the dirt...I can't afford tires every month.
That said, I havent been a to find any past threads discussing this issue or a resolution. Does anyone have any tips or experience here...or help guide me to a past thread with info. I've driven my truck pretty hard in the dirt for several years without issue, until now. Could it be the external actuator taking a dump (please say no...they're about $1100)

Thanks!
Jake

 

Damn it sounds as if (maybe) the rear differential may have gone out. It happened to me and the same thing happened. I had a 2005. When it happened to me though, I heard a pretty loud bang when I thin it went out.

 

I haven't driven that far trying to engage, nor driving like this ~. I'll go give that a whirl right now.
I have used the system monthly over the years, and kept it maintained. Fingers crossed I just havent driven far enough

Geez I hope not, thankfully no loud mechanical noises at any point. And drives great in 2wd

 

No luck unfortunately. After the current rain, I'll pull the skid plate and take a look at all the diff connectors and equipment
Thanks for the input