OK, but what about us older Blazers?? I have a '96 that I am trying to troubleshoot for what appears to be an uncommanded engagement at highway speeds.
What happens is that while running at 55 mph, occasionally a high pitched whine starts and then gradually gets lower and loud as heck. I pull over down to 10 MPH, hear a loud clunk and all is well.
I pulled the battery, and checked the function of the vacuum actuator and when I start the motor and have someone switch the electrical switches in the cabin from 2wd to 4wd nothing changes. There seems to be vacuum at the actuator at all times. There is an electrical switch that is supposed to control the vacuum right behind the battery.
The question is, when is the switch supposed to supply vacuum to the actuator? in 2wd or 4wd? When choosing 4wd, is that switch supposed to have 12v applied to it? Maybe I'll apply 12v directly from the battery and see if it works.
I should also mention, that when driving in snow last weekend, the 4wd function DOES/DID work.
AJ