Trooper 4wd takes a while to engage

It used to work flawlessly for two years. Now the winter is coming, and I wanted to test out shift-on-fly 4wd on my Trooper 98. The problem is that most of the time it will take 2-3 minutes to engage, green light keeps
blinking all the time. Sometimes it kicks in within 5 secs, just like it used to do all last winter. Mechanic checked the darn thing and can't find anything wrong, it seems to engage just fine when in garage, and vacuum sucks as it should.
Any ideas what could be wrong? I'd rather fix it before snow comes.
Peter
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No help, but I have the exact same issue, happens most during hot weather, not cold. Have found that sometimes turning vehicle off with 4WD button engaged (but light still blinking) and waiting a bit, it'll start up engaged then, but its not reliable.
I'll be watching this thread hoping somebody has an idea, as it drives me crazy when it happensn
Peter wrote:

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