I have a 91 4runner and my 4 wheel drive stoped working. I found the problem and just had to replace a bad vacuum hose that hooks up to the front diff . Now when I shift into 4x4 the light flashes like it's going in then shuts off right away. I checked to see if the 4x4 is working, but it's not. I still have vacuun suction on the diff, and if I remove one of the smaller vacuum hoses on the ADD (I think that's what it's called) diff the 4x4 works and the light comes on. Does anyone know why this might be happening, or how to fix it?

 

check to see what sides the hoses are going to. mine did this and it ended up being that they where backwards. the suction in 2wd should be on the out side or side away from the electrical connection on the actuator. and 4wd the other side. also if they are right then look at pulling the sensor on the front and with it in 4wd if the rod and fork slide over into position if it does then check continuity at the switch.

 

Thanks, I'll check it out.