2000 4runner 4Hi doesn't work but 4Lo does

[PrinceYota]

I have an Automatic 2000 Toyota 4Runner SR5 3.4L V6 and recently I noticed that 4Hi isn't working. The indicator light comes on but 4Hi is not operating and not engaging but 4Lo works. I've been told that if the 4x4 indicator light comes on but the front doesn't engage it could be the Front Differential Actuator. I'm aware there is also a Transfer Case Actuator. What is the difference between the two and what are the malfunction symptoms of the two? Can someone shed some light and chime in on what may be the cause.

 

[TheDurk]

Well, if 4Lo works, neither actuator itself is the problem. It's in the vacuum and electric controls that make them work. One way to diagnose is to put the truck up on jackstands and engage 4H. If the front shaft spins, but the front wheels do not, then the TC is engaging, but the front diff is not. If the front propeller shaft does not spin, then the problem is on the TC side. Shut the engine off and try to turn the shaft with your hands. You should be able to tell if the front diff engaged.

Are you absolutely sure your 4H is not engaged? If the 4x4 light is on, the sending switches on the TC and the front diff both must close, signalling mechanical engagement. Again, putting the truck on jacks will settle this question as well.

That's as much as I can tell you, as I have the 5-speed with J-shift and no TC actuator, so it's very different from yours in the control circuit.

 

[PrinceYota]

So I put it in 4Hi engine off and front-end jacked up, and the front propeller does not spin by hand. 4x4 Indicator light is on. I had an assistant put the vehicle in 4Hi driving back and forth with me checking underneath the car and the front propeller does spin. Would this indicate 4x4 is working properly. Shouldn't the front wheels spin together by hand if it is in 4hi with the car in the air?