green 4 wheel drive light doesn't come on, 4 wheel drive doesn't engage

[4Runnerswa]

Hi

When I select 4 wheel drive with the shifter (no button) the green light in the dash does not come on and I can tell that the 4 wheels are not engaged. ie The steering doesn't stiffen up when making a tight turn.

I think it might be an electrical problem because in the past when I engaged 4 wheel dr, there was a audible click from under the dashboard, on the passenger side of the truck and the light would come on.

Any ideas?
Thanks

 

[JMunn55]

It's an auto disconnecting differential issue. Either a vaccuum leak, a Vaccuum Switching Valve issue, or the electronics going from the shifter to the VSV. I'm trying to fix mine now, it's doing the same thing. I replaced all the vaccuum lines going to the front differential and the VSV

 

[revenantdead]

check the 4wd relay. its behind the passenger side kick panel.

 

[TheDurk]

Here we go again, my standard post:

Don't guess at it, troubleshoot! Start at the twin VSV's (Vacuum Switching Valves) on the driver fender wall. There are two long vacuum hoses that come up from the diff, one goes to each VSV. Check to see that one of the two hose nipples on the VSV’s has vacuum (engine running, 4WD NOT engaged. If no vacuum either side, check the check valve going to the intake manifold and look for loose hoses or a hole in the reservoir. If there is vacuum going to one hose, then put it in 4WD. See if the vacuum switches to the other hose. If it does, and no 4WD, problem is the diff actuator or the line to the diff. If it does not, then just switch the hoses and you should go into 4WD. This confirms diff is okay. (Mark the hoses first so you know which belongs where!)

OK, switch them back. Then use a test light to see if electrical signal from the TC also switches sides of the VSV. If it does not, problem is the TC, the switch on the TC, or the TC actuator, or its wiring back to the button (last two for non-J shift only). If it does, but the vacuum does not, the problem is the VSV itself.

I start troubleshooting at the VSV's because you can figure out where the trouble is without having to climb under the truck. [Does not apply to '01-'02]

 

[Gerdo]

My light doesn't go on either but I know I have 4wd.

What transfercase do you have?
If you have a center diff locker (this locks the transfercase, front axle to rear axle). If that is unlocked, you won't have the drivetrain bind on dry roads.
Go to a parking lot and shift into 4wd and turn fairly hard (right or left doesn't matter). If 4wd is working, you will have drivetrain bind. If you have a center locker, this must be locked.

 

[JMunn55]

I replaced all of my vacuum lines, now the light does come on. Haven't had a chance to test if 4x4 works yet. (when I realized it didn't work I was in snow - only rear wheels would spin/no light on).
It's likely fixed, but if it isn't, the fuse is the next thing I'll check

 

[Rocky5000100]

My 3rd Gen doesn't always engage immediately. I have to put it in neutral or reverse, and then back to drive again. Also try driving forward slightly.

 

[JMunn55]

It works now. Green light came on, and the front wheels definitely spin. It was just a vacuum leak for me