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.

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...