Won't go into 4 wheel drive

Hello there.

I just experienced a problem - I can't get the truck into 4 wheel drive.

The floor shifter moves into position, but I don't hear the relay? and the indicator light doesn't come on.

I've had in the past where I hear the relay click on / off a few times but then the light comes on and all is well. But today, nothing. I've tried even putting it in 4 low with no success either.

Is there a linkage that could be out of adjustment? Where exactly is the realy - sounds like it was behind the glove box.

HELP!

Where do I start to look...

Weather is brutal and the truck is even worse in 2 wheel drive!

Thanks for your help!

Could be a leak in the ADD, it uses a vacuum to engage the hubs. Especially since you have heard the 4wd try to engage (click) multiple times before it actually gets the hubs to engage. You should have one click and then the engagment.

Or check the fuses first in the passenger compartment and then in the engine compartment. (if any are applicable)

Sorry to sound like an idot, what is the ADD?

I'll check the fuses first.

Does anyone have a schematic or drawing of the 4 wheel drive system? Maybe a picture of the linkage too?

I'm not positive of what i'm looking for...

Thanks

Oops!

Yea, now I do feel like an idiot... Just a simple spelling mistake...

OK.

I have a 99 4Runner V6, SR5 automatic. Not the limited model.

The shifter is on the floor. I'm not sure about the automatic disconnecting differential. How do I know if I got that?

Back into the cold, frigid, icy garage. That'll be my excuse for further spelling mistakes...

The ADD is the automatic disconnecting differential control system. It allows us to engage our front hubs without getting out of the car like old 4wd systems. This causes our front driveshafts to spin all the time which is one downside as well as the fact that we have vacuum lines that must be airtight to engage the front hubs.

The ADD system is pretty complex to diagnose yourself, It involves checking the solenoids, actuator, switch, tank and vacuum lines. I would recommend taking it to a 4x4 shop.

The relay is somewhere behind around the glovebox, that is all my diagram shows. There will be 5 terminals in it
1-3 in the top row
4-5 in the bottom row
EX:
1 2 3
4 5

1. verify continuity between 1 and 3 and between 2 and 4
2. use jumper cables, connect positive lead from battery to terminal 4 and the negative lead to terminal 2 of the relay and verify continuity between 3 and 5

If it doesn't operate as described, replace.
Hope this helps.

Thanks for the information.

My fuses are fine. ADD fuse is fine.

Linkage is internal. Can't see it from the bottom or when I remove the interior pieces.

Next, I'll try to locate the relay. I used to hear it behind the glove box, but i'm not sure exactly where. I'll try to locate it and test it.

Is there a diagram for vacuum lines etc?

Thanks.

I've searched everywhere.

Here's what i've come up with...

Vacuum leak
Actuator gone bad
Electrical problem

These are from different posts here. So, now what?

Is there a service manual here posted somewhere?

4wd worked last week... Now, nothing.

Anyone have any ideas of where to look? Where are the vacuum lines? Where is the actuator and the electrical components?

Thanks...

i have a 96, and i know the 4wd systems are different, but i have to drive a ways b4 it will engage, is that the same with the newer 3rd gens?

Maybe a delayed reaction, but it always came on within a few moments. The 4wd worked last week. Off and on the last while it would "click" a few times (from behind the glove box) and then the light would come on and away I went. Today, nothing. Maybe a click in the beginning, but the light never came on and it didn't go into 4wd.

I'm unsure of where to look on the truck. Where is the actuator? Where are the vacuum lines? Where is the relay, other than behind the glove box somewhere. I took out the box, but couldn't see the relay. I really don't want to take it in to the shop - i'm sure if I knew where these pieces were, I could figure it out. I've read tons of posts about what possible problems it could be. I'd like to start at the easiest/most probable one first and work from there.

If anyone has a picture of what to look for or a diagram etc, it would be a great help.

Thanks again for your responses.

lets see what this mechanic can dig up???

The 4WD ECU detects the condition of the detection SW ((Shift diff lock), (Transfer diff. lock), (Transfer H2, H4F)), 2-4 select SW and the vehicle speed, and controls the 2-4 select motor and VSV ((2WD, ADD), (4WD, ADD)).

4WD CONTROL


1. Shift position
The target shift position determined through the condition of the 2-4 select SW and detection SW (Shift diff. lock), and operates the 2-4 select motor.

When the 2-4 select SW and the detection SW (Shift diff. lock) are both OFF , put in to H2 position. At this time, current flows from the 4WD fuse to TERMINAL 12 of the 4WD ECU to TERMINAL 26 to TERMINAL 2 of the 2-4 select motor to TERMINAL 3 to TERMINAL 13 of the 4WD ECU to TERMINAL 25 to GROUND , so the 2-4 select motor rotates at H2 position.
When the 2-4 select SW is ON and the detection SW (Shift diff. lock) is OFF , put in to H4 position. At this time, current flows from the 4WD fuse to TERMINAL 12 of the 4WD ECU to TERMINAL 13 to TERMINAL 3 of the 2-4 select motor to TERMINAL 2 to TERMINAL 26 of the 4WD ECU to TERMINAL 25 to GROUND , so the 2-4 select motor rotates at H4 position.
When the 2-4 select SW and the detection SW (Shift diff. lock) are both ON , or the 2-4 select SW is OFF , and the detection SW (Shift diff. lock) is ON , put in to H4L position.When switched from H4F to H4L, current flows from the 4WD fuse to TERMINAL 12 of the 4WD ECU to TERMINAL 26 to TERMINAL 2 of the 2-4 select motor to TERMINAL 3 to TERMINAL 13 of the 4WD ECU to TERMINAL 25 to GROUND , so the 2-4 select motor rotates at H4L position. When switched from H2 to H4L, current flows from the 4WD fuse to TERMINAL 12 of the 4WD ECU to TERMINAL 13 to TERMINAL 3 of the 2-4 select motor to TERMINAL 2 to TERMINAL 26 of the 4WD ECU to TERMINAL 25 to GROUND , so the 2-4 select motor rotates at H4L position.
2. Shift limit control
When the vehicle speed is over 100 kph , shift change to H4 or H4L mode can not be made. The vehicle speed signal is input to TERMINAL 3 of the 4WD ECU. At this time, the 4WD indicator light and the center diff. lock indicator light flashes, and the buzzer installed in the 4WD ECU goes ON . This condition can be canceled by decelerating the vehicle speed to below 100 kph , or by selecting H2 mode.
3. Shift control
When the 2-4 select motor will not switch after approximately 3 seconds from shifting (When there are no changes to the signals to TERMINAL 8, TERMINAL 9 and TERMINAL 22 of the 4WD ECU), the 4WD indicator light and the center diff. lock indicator light flashes. The cruise control is canceled if in use. When the 2-4 select motor switch is completed, the indicator lights go OFF and the cruise control can be set again.
4. ADD valve control
When switching between 2WD to 4WD, the VSV is controlled to free or lock the ADD. At this time, current flows from the 4WD fuse to TERMINAL 12 of the 4WD ECU to TERMINAL 23 to VSV (2WD, ADD) to GROUND , or flows from the 4WD fuse to TERMINAL 12 of the 4WD ECU to TERMINAL 10 to VSV (4WD, ADD) to GROUND , so the VSV (2WD, ADD) or VSV (4WD, ADD) is controlled.

the 4wd is not controlled by vacuum

I have no idea if this will help but I guess it cant hurt.

<a href="http://s122.photobucket.com/albums/o262/Alistor01/?action=view&current=4wd_ecu_p196.jpg" target="_blank"><img src="http://i122.photobucket.com/albums/o262/Alistor01/4wd_ecu_p196.jpg" border="0" alt="Photobucket"></a>

Thanks.

Where will I find the 4wd ecu?

So, it's not controlled by vacuum then?

Darned electrical stuff...

Hey Alistor, I see you're in Vegas. My favourite place...

How's the weather? Love to move there...

Torinate said:

Thanks.

Where will I find the 4wd ecu?

So, it's not controlled by vacuum then?

Darned electrical stuff...

Hey Alistor, I see you're in Vegas. My favourite place...

How's the weather? Love to move there...

Click to expand...

I am not an expert on toyota electrical by any means, in fact I know VERY little. So Im sorry I cant help you with the 4wd ecu. I just got my first T4R and am in the process of taking it apart and learning all its ins-n-outs.

Vegas is great I just moved here from Southern California. Lower cost of living and no state income tax are good selling points. Weather right now is 70 and sunny! Good luck with your 4WD system...

It is Vacuum for SURE. The solenoids (2) mounted together are under the center console area under the truck. The actuator is on the front of the transfer case as well as the switch. Each of these needs to be checked. The vacuum lines connect to the actuator and solenoids so that is a good place to start looking.

If you have the 4wd button on the side of your transfer case shift lever you have "One-touch" or 4WD shift selector system. That contains some more electronics like a 4wd ecu that only the dealer can service. I thought those are only on limited models and you said yours is sr5 so you should have the normal shift on the fly 4h/4l/2h lever. They are slightly different systems.
If you really need direction as to the diagnostics a Haynes book is a good buy at 20 bucks.

I have a 1996 4 Runner 3.4L 4WD Automatic. I am having a problem with the 4 WD. I move the selector to 4H, the transfer case engages but I get no output at the front wheels, I can shift the selector to 4H or 4L transfer case engages always. Would like to know what I should check. Everything physically appears to be correct.

dalemanning said:

I have a 1996 4 Runner 3.4L 4WD Automatic. I am having a problem with the 4 WD. I move the selector to 4H, the transfer case engages but I get no output at the front wheels, I can shift the selector to 4H or 4L transfer case engages always. Would like to know what I should check. Everything physically appears to be correct.

Click to expand...

Sigh...my standard post....

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.

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 switch on the TC. 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.

Click to expand...

TheDurk said:

Sigh...my standard post....

Click to expand...

Thread revival warning.

I'm getting a blinking 4wd light at all times (2000 limited with push button and J-shift).

The problem started 4 days ago and it happened for just a minute then went off. I didn't feel 4wd engage but my butt gauge isn't the best at resisting influence from an overanalyzing mind. It did this on and off over the weekend and eventually just has gone to where it constantly blinks and I'm getting no 4wd engage.

So tonight I've tested the vacuum on the VSV's and the vacuum isn't ever changing sides regardless of what I'm doing with the transfer case. So I switched the lines to pull vacuum for the opposite side hoping to engage 4wd and rule out the front diff but I still had no change. So now I'm completely stuck in my troubleshooting.

I've also pulled and checked continuity on the front diff locker sensor as well as the two on the back of the transfer case actuator... all three are getting continuity when the plunger is pressed in. I'm also not hearing any change when I press the AWD button or when I shift into 4-hi or 4-lo (well, not outside of the actual shifter linkage making noise as I move it around).

Any idea where I should be going next?