96 gmc 4wheel drive not engaging

You must scan the system with a special tool as it is computer controlled.

the hub actuator for the drive at the hub is either no engaging correctly or is failing in the engagement allowing it to jump in and out of engagement
check for full engagement or replace worn or broken parts in the hub drive

When ever that light comes on and blinks there is a fault. Take it in to get serviced.

4wheel drive wont engage on 1990 GMC sierra 2500 what could the problem be ,if it is acutator where is it located

Dave,
The problem your are speaking about could be a few things. All things that are somewhat common to go bad on Chevys/GMCs. Each one of the cars I worked on had a different problem. I have changed the switches, the 4wd solenoid, and TCM on different trucks. IMO the TCM location in the passenger kick panel is a poor location allowing water and other passenger debris to get into it. Once water gets in that area you can imagine already what occurs. One of the cars the TCM bracket was rusted by the ground and eventually the weak ground fried it. The weird thing is the TCM would allow it to shift sometimes and not other times or partially engaging causing the wonderful light to blink rapidly. What I have found of some time with these trucks is pushing the button to change the truck to two wheel drive and driving a few feet in reverse helps ease the change.

So you can start with a new switch that pops in and out of the dash in a few mins. Can get one on ebay for under 25 dollars. Although, I personally would take off the kick panel and take a look at the TCM. If you see any rust around it, my money would be on that.

Good luck

what's wrong with 4wheel drive when light blinks on 4hi other than not engaging

not a fuse if you have power to switch,if your 4wheel light does come on and is not blinking,check the little motor on the transfer case,tap it while someone tries the switch,it might just be stuck from not being use,if it doesn't free its self you may need to replace it.

is it because your not at a stop?

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,

The light blinks to alert you that a problem exists in the control module for the 4X4, contact expert Toyota Ed he is the service manager of a Toyota dealer, he knows his stuff