Check the fuses.
SOURCE: 1990 GMC Sierra 4x4 1500
the connections near the front axle that activate the motor to engage the system aren't melted? That's a comon problem for that body style. If there good, sounds like it could be that motor itself. To figure out if it's you motor or transfercase, jack up the rear end, have a friend inside shift into 4 wheel drive, or try to, and put it in gear and apply some gas. If the front driveshaft is turning then it's something with the front end. If not, farther back in the system.
SOURCE: 97 JIMMY,PUSH 4X4 BUTTON,NOTHING HAPPENS
I had the same problem with my 99 Jimmy. try to disconnect your battery for about 5 minutes and see what happen. it fixed mine by doing it.
SOURCE: 4x4 will not engage in 96 gmc yukon
I just fixed a friend of mines 96 yukon...shift to neutral press 4H and u can hear the actuator make noise (we even replaced it with a new one his idea and the same thing happen as old one), so as he hit the switch for 4H i layed under it (on 4 jack stands) and I could hear the motor on the transfer case make a loud noise (well thats working) and before all this I asked him did u check all your fuses (he said guarnteed to be all good) one night it was bothering me so i looked through the owner manual for the yukon and in the fuse box on driver side by the door there are (2) fuse for the 4wheel drive unit,pull one of the fuses good...pulled the other one and it was blown put in a new fuse and it works like brand new..pull fuse for anything that has to do with 4 wheel drive componants,
SOURCE: 1995 gmc yukon wiyh 6.5 diesel 4 wheel drive will
On the full size, the front actuator is electric, not vacuum.
When in 4wd mode, a switch on top of the transfer case conducts 12
volts out to the actuator. Wire #50 (brown) is the 12v feed, and it
conducts to the light blue wire (#900) to the actuator.
When shifted out of 4wd, the switch opens up and no voltage goes to the actuator.
Check voltage at the connector for the front actuator (at the
front differential - it looks like a large bullet that threads into the
front diff.) If it has 12 volts, the actuator is the problem. If it
does not have 12 volts, check the transfer case switch and the power
feed to the transfer case.
I'll assume it is the actuator, if the plug to the actuator is getting 12 volts when in 4wd.
The way this actuator works, is it is a sealed chamber that gets heated
by voltage. When it heats, the pin in the end swells and pushes a shift
fork in the front differential. The shift fork engages a spline on the
passenger side of the differential, and boom! you have 4WD.
GM offered an upgrade to this actuator that is a motor instead of a
heated device. However, it requires a small harness addition, a spacer,
and a new actuator. It is about a $150 to $200 option.
If I were you, I would buy a new heated actuator. They are available at
most auto parts stores, and are about $90. They are also on eBay for
about $55 plus shipping. These are very easy to change - just thread out the old one, and thread in a new one.
Good
luck. The actuator is usually the problem 90% of time but recheck all
of the wire harness just to maker sure there is no short before
replacing any parts.
Testimonial: "This is exactly the info i need to troubleshoot and repair efficiently complete with wire numbers and colors thanks for the help buddy"
SOURCE: 4x4 push button is not working about how much does
This is something you can do yourself if you have ever worked on a vehicle before. The part you need is called a front drive actuator valve. It costs about $ 50.00, GM part # 15165891.
Here is some more infor about it:
Main 4wd Components:
TCCM - Transfer Case Control Module - Located behind the glove box. This is the electronic 'brains' behind the shifting.
Switch - The push button switch in the dash - driver input/indicator.
Encoder Motor - Located on the transfer case - This is what actually shifts the transfer case, and tells the TCCM what position it is in.
Vacuum Switch - Also located on the transfer case - This is what sends vacuum to the vacuum actuator (see below) when the transfer care is in 4HI or 4LO.
Vacuum Actuator - Located under the battery tray - This is what engages or disengages the front driveshaft.
Front Axle Switch - Located on the front axle - This is what tells the TCCM when the front axle is engaged.
If you want to try and replace it yourself, please let me know how it goes.
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The 4wd switch on the inside might be out
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