If you have the Auto4wd option (switch as shown in tjmicsak's post above), then you have the electronic solenoid which allows vacuum to flow to the front axle actuator. It will be located near the distributor on the firewall. Someone may have removed the solenoid there-by leaving the front axle engaged all of the time, however, this is not the same as having the transfer case in 4HI all the time.

If you do not have the Auto4wd option and have only 3 buttons on the 4wd switch, then the vacuum switch will be mechanical and it is located on the transfer case itself.

With the front axle engaged and barring any other problems with the front driveline, the only real symptom you would experience would be decreased mileage due to added drag in the driveline. If the transfer case were locked into 4HI all the time along with the front axle being locked in, then you would have binding while turning on high traction surfaces.

What lights are on in the 4wd switch in the dash? What happens when you press one of the non-lit buttons?

 

Hi, im new to this forum and also to the 4x4 Blazer world since today!, but... i have a tranny problem similar to the one in this topic, does anybody have updates about it?, my ZR2 has the automatic 4x4, four buttons, and all the lights are on, pushing any button its no use they stay lit, the truck drives but very slowly and i just drive at 30 mph and sometimes smells like burn tire (im not an expert obviously), im not moving the truck until i fix it.

Ill continue looking on older topics (there is a lot of them!!!) or maybe post a new one .

 

well finally got everything sorted out (well... mostly everything) 4wd is fixed...had a bad encoder motor AND a bad dash switch (2-hi lite did not work)....also had the seal replaced between the tranny and the transfer case (was overfilling transfer case) vac. switch was good (Oh joy! cheapest part to replace and it was good) best part of the ordeal was finding the proper encoder motor on ebay for 100 bux. (thanx to all the forum help).... oh... and fixed my horn that hasn't worked since i got the truck last august... who knew all I had to do was get PO'd at some idiot on a cell phone and slam my hand down on the steering wheel... to my surprise it started working.... made me happy! now all I need is to have the front diff axle seals (all 3) replaced (leaking like a sieve)... got a price from a shop ( my guy doesn't want to rebuild them)... they wanted $175 a seal? $525 bux? If I can find a good used one (or a cheap new one?) my mech. will put it in for $50 bux.... ok... this is long enough you've been updated.