I know I know another 4x4 not working thread. I searched but figuring giving my specifics would aid troubleshooting.

Let me start off by saying I'm new to this forum, Toyotas and off-roading all together. I come from the land of lowered German cars. Love the forum!

I just bought a 99 SR5 3.4L auto less than two months ago. Let's just say it's been fun and I've learned a lot. Once I get the bugs worked out it should be/hoping I'll have a great rig.

It's very cold here the last 2 days -34 Celsius. Have used 4x4 several times since the purchase. Went to engage on the fly today to 4hi and it had a hard time going in. It did not engage at all, no light. Tried messing with it. Stopped and tried it in 4lo. Grinder a bit, was probably nervous and frustrated. Will go into low gear but will not engage front driveline and again no light. Tired it some more driving and stopped, J shifter moves smoothly between 2hi, 4hi, N and 4lo. I can hear like a switch clicking between shifts as well. No grinding or out of place noises

Any help would be greatly appreciated! Less of me freezing my ass off or dealing with 2wd on glare ice

Almost seems like your ADD doesn't work - the front axle disconnect. May have to check vacuum lines that go to it, if it's not actuating. Others will chime in that are much more knowledgeable about the issue, and the ADD.

I came from a world of lowered Hondas not too long ago. Isn't this community so much better ahah?

The relay that is clicking is the one in the passenger side. I'm assuming that the issue is down the system more, at the VSV or actuator.

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I too came form lowered german cars, that and lowered Volvos, and a nice DD Toyota corolla wagon, which I wish I had never sold.
I would bet that its in your vacuum system, I will try to find the thread that
TheDurk helped me with the same issue a few years back.
Mine ended up being a stuck vacuum check valve, again after the Dirk told me how to trouble shoot

VSV’s/ADD
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. [None of this applies to '01-'02 which have an electric actuator.]

***********************************

the above info is courtesy of TheDurk in a thread I started years back


I hope that helps, this was back in 2015...title of thread was no 4wd
and a thread I started. NOt sure hwo to link the thread , but I bet you can find it under my name or the title in the search, but you will have to go back a bit....like I said 2015

also another issue I had recently with it not working, I had knocked off a vacuum line while doing an oil change, it was at a junction box below the big black vacuum box where a bunch of hoses come together like between the battery and the box and lower.
how I knocked it loose I don't know, 4wd worked the night before, did an oil change, went for a drive, no 4wd, came back retraced my "oil change" and found the hose knocked loose.

also , way back, I don't remember if the light was coming on or off when it was not working. It made all the clicking sounds, like you are hearing.

the vacuum check valve was not cheap, in that thread I believe it tells you the size etc you can get, I could not find the exact replacement without going to Toyota, so I found one at napa, it had one line in , 2 out, and I capped one of them off.
since then I went with Toyota when I was ordering tons of stuff from camelback

Thanks for the help folks. I'll see what I come up with

I found this as well going to troubleshoot tonight

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Had the exact same issue when we put our '98 together - one of the vacuum lines wasn't connected. Popped it back on and all was well.

Probably something like this.

The relay clicking in the passenger footwell tells you that the switch on the transfer case is working. The relay switches power to the ADD VSV's in the engine bay.

Check the vacuum line off the manifold (comes off the front or the rear, depending on year) that goes to a one-way valve (1/2" dia canister in the vacuum line run), then down to a multi-connector. One line goes to a large vacuum canister in the fender well, the other two outlets go to the two VSVs below the fuse box. Check all those connections.

Here's the canister in the wheel well:


-Charlie

Vacuum lines seem to all be attached, at least from the vantage point at the top. Comes off manifold goes to VSV and canister, which does not appear to have any visual holes. Maybe the blue check valve, VSV itself or something in diff

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Did you try driving around a corner? Does the front drive feel like it is engaged? It might just be the ADD position switch that actually turns on the light on the dash.

-Charlie

Most definitely not engaged, lots of snow and ice. Truck is very tail happy

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The check valve is working

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Ok... with the shifter in 4H, verify that the front driveshaft is locked (truck can be off).

Check for 12V on the ADD VSV connectors. One should have power and the other should be off. Verify that they swap when the shifter is moved from 2H to 4H - the truck will need to be on for this test.

-Charlie

Checked VSVs they are switching vacuum properly. Will check driveshaft tomorrow. Narrowing things down at least lol. Must be the actuator or line to it.

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