Short version: Son picked up a 96 Limited that needed some work. It's in the garage at the moment to have the gas tank repaired (the one "surprise" ... top of the tank was in bad shape) but we're planning on doing most of the work ourselves when possible.

We've done some basic diagnosing of the 4WD problem, as follows:
*4WD icon on dash doesn't light up. Drove on snow, most definitely not in 4WD.
*Press the button, hear the transfer case engage.
*Physically checked the drive shaft. When engaged, the front drive shaft locks in place. Rotates freely by hand when in 2WD.
*Reversed the vacuum hoses under the hood (drivers side fender) which supposedly "forces" the front diff to engage. No dice.

What would you suggest as the next step?

I'm thinking we need to verify if the hoses are actually providing/getting the vacuum. Is there a quick test for this?

I'm relatively mechanically inclined, but full disclosure, I don't know 4WD systems all that well. Maybe there's something simple/obvious that we're missing?

There is a plug with a sensor on it on the front diff, in many cases that sensor gets fowled and can’t get signal. I would pull the sensor out and test for continuity.

Here is a link to a 99 limited, which is a similar set up to your 96, that had a problem with the sensor I mentioned: 4WD won't disengage on 99 4Runner LTD - YotaTech Forums

With what you've stated look toward the vacuum actuator system on front diff.
Solenoids have been known to not shift, hose damage to actuator, actuator itself.
The 4x4 indicator won't show till front diff engaged.
If you haven't download the FSM good troubleshooting info there.

This should be your next step. The test is to employ your Mark I forefinger and feel if there is vacuum on one nipple on the VSV going to the diff hose in 4wd and on the other one in 2wd. If the vacuum is switching, but diff is not engaging, your actuator on the front diff is your prime suspect, assuming the hoses are good.

It should be obvious, but engine needs to be running. Forgive me, but the internet doesn't show how much you know.

one of the hoses on mine near the back drivers side of the intake manifold popped off and my 4wd did the exact same thing

Any updates on the issues?

In that case the Mark I finger would just feel a weak vacuum or maybe none at all, but one that switched to the extent it is there. The actual vacuum feed to the ADD is from the front of the manifold.

I bought my 97 a year ago and no 4wd light. No relay click or anything. I replaced the sensor on the front diff. (I pulled the hoses off)


Sill nothing.
I pulled the Transfer case actuator off a known working 4runner, Bingo the relay was clicking and I could here the motor working on the Transfer case....But still no light and no 4wd.



So today I took the front diff actuator off and I couldn't move the shift fork without a lot of force from my hands. Seems like it should move ease since its moved by vacuum. Took it apart, cleaned everything out and lubed with fresh gear oil. BTW, You can take it out without dropping the diff, just takes an angle and twist. Now it would easily slide.





Now I think im in business right? WRONG! Still no light.
Then it hit me. The truck I took the TC Actuator off was in 4wd when I removed it. mine was in 2wd. Removed the actuator, pushed the button in on the shifter, pushed the rod in (Manually engaged 4wd at the TC), reinstalled the TC Actuator motor...….Then this beautiful thing happened....



I hope this helps you. It was a very long and frustrating road for me. The manual says to exercise the 4wd regularly. Taking all these pieces a part you can see why. They are all lubricated from the system actually turning. I think besides the TC Actuator being off taking the Front Diff fork off and cleaning it was the key. I checked all fuses, hoses, and sensors as well.

Sorry for the delay in updating... got caught up with life getting in the way.

In short, it was the 4WD VSV that was dead. For some reason this little plastic valve is over a grand from the dealer... $1420, if I remember correctly. (Translation: We don't really want to be bothered with parts that old... go away.)

So, our garage bought 2 of the equivalent parts from Ford for $58 each and jury rigged them in place of the OE ones.

Works like a charm.

Nice! Good work! If you do want and OEM one I’ve got an extra in the garage I’d be willing to let go!

Those are the types of things I grab when I go junking.


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I'm lucky this post is recent because I'm trying to diagnose my own 4WD problem:

Truck: '99 3.4L SR5 4WD 4Runner

Background: Doesn't shift into 4hi and 4lo after I got stuck mudding a few months back. Truck was sitting in muddy water well up into the engine bay for a few minutes which messed up some other things as well (starter, ABS module, gas gauge). So I think the problem is related to wetting out something in the 4wd system. When I pull the lever from 2hi to 4hi, I feel the usual resistance like something is engaging, but I don't get the dash light and I don't think I'm in 4hi because the steering isn't tighter like it usually is.

Diagnosis so far: 4WD fuse by driver side door is good.

Tried checking the VSV hoses today. There is vacuum from the intake but it is pretty weak. The check valve in the intake line seems to reduce the suction by say 50%. Not sure how strong the suction needs to be. When I switch the hoses going to the diff, 4WD doesn't engage. I checked the hoses where they connect to the diff, and both seem to maintain the same (low) suction so I don't believe there's a major leak in any of the hoses. When I switch to 4wd I don't get suction from the other port of the VSV, so that's problematic too.

What's the normal amount of vacuum/suction in the VSV lines? I'd like to rule that out before I dig deeper (opening up / replacing the actuator). Any other thoughts welcome. I'll think twice before mudding again

Especially recently there has been a plethora of 4wd issue threads. Searching is your best friend. A quick google search can help quite a bit. But to aid in your question. I believe that it only is supposed to have 9 lbs of vacuum, so relatively weak. With the depth of the mud I would highly suggest that you change the fluid in the transfer case, there is a breather on the top of it that by the sounds of it were clearly submerged for a prolonged time. Change the fluid and check back.

It could also be that your front diff is now full of mud and the sensor on the front diff is junked from it also. So pull the sensor and check it for continuity.
Also if your truck is an sr5 there should be no actuator on your transfer case.