Chevrolet Repair: no 4 wheel drive available, obd ii, s10 blazer

Question
Hi cjs,

 I have a 1995 cheve s10 blazer 4x4.  The four wheel drive is not engaging, but the selector switch on the dash is not illumiated and when i push the button nothing happens.  was just wondering if the switch could have gone bad or if this is some other type of problem with the 4 wheel drive.

Answer
Hi Vince,

The switch can go bad.  Is that it, I don't know, but am not leaning that way yet.  

You can switch to hi 4x4 while moving or stopped.  Does this not engage either way?  Can you get it to low?  That is done stopped and in neutral.  Push up once, then down on the switch.  If you try this and the lights blink, then you have a problem.  

Your system is a 'motor' on the front axle, and an actuator in the transfer case.  The 'motor' can be vacuum operated or electrical.  If electrical, check for current at the plug.  Unplug the harness, and use a test light to see if current is present at either of the prongs comming from the harness.  There may be a switch on the axle that tells the button on the dash the 4x4 is on.  This may be corroded.  If vacuum operated, check for vacuum on either side of the 'motor'.  Then test the diaphram of this 'motor'.  If it is ripped, it won't hold vacuum from a handheld vacuum pump.  

If there is a failure in the system, usually the switch lights will blink.  Since they are not, possibly it is the switch.

See if you have free place who will check your OBD-II computer.  It may tell you something.  We have Autozone here in Michigan.  They will scan your computer for free, in the parking lot.  Then hope to sell you something.

Hope this helps.

C J S