4wd not working

Hi guys, I need some help trouble shooting my 4wd. I have a 99 Tacoma TRD off road with the a.d.d. When I push the 4wd button the light on the dash does not do anything, no flash and no chime. The transfer case engages the front drive shaft but the front axcel doesn't engage. If I push the 4wd button while moving some times I don't hear anything and the other times I hear a grinding noise like my front axcel was trying to engage but can't. I have checked the a.d.d. fuse and I have also taken off the 4x4 actuator from the front drive shaft to inspect it. Both fuse and actuator appear good. Has any body had these issue's or can someone please point me in the right direction. Thanks.

 

By this, I am assuming you mean the actuator on the transfer case, yes? If so, and that one is working, my immediate thinking, based on what you mentioned, would be what my issue was. Mine was the ADD actuator itself.

Just to get a few things squared away, try these and see what your results are.

With the truck on, shift the 4WD lever into the Lo position but without pressing the 4WD button. If the 4x4 light comes on and 4x4 engages, good chance it's your switch.

With the truck on, go underneath and disconnect the plug for the t-case actuator. Go in the cab and look for the 4x4 light. It should be blinking, indicating a problem. Now plug it back in.
Next unplug the ADD actuator and see if the light comes on in the cab. If it does not, it's almost guaranteed it's the ADD actuator.

If you wanna do another test, try this. With the truck on and 4WD not pressed, disconnect the ADD actuator plug. Now go in the truck and press the 4WD button. If you hear the t-case actuator function, that's even more evidence of a bad ADD actuator.

Here is a picture of the ADD actuator I happen to have, in case you're not sure where it is.
This is underneath the truck, looking towards the front. The tube looking part down bottom, with the blue/white sticker is the steering rack, and the large grey part atop the picture is the transmission (I have a manual, so this may be different for you). The ADD actuator is on the back of the front differential. If you have factory skids, you won't be able to see this area from directly below without removing them.



My post might be a bit incoherent, but I hope it helps. If you have any questions, I will do my best to answer them.

 

Thanks for the reply, by the 4x4 actuator I meant the a.d.d actuator off the front drive shaft. Mine looks different then the one in the picture but it is located in the same location.
When I put the 4wd lever in 4low without pushing the button the light still doesn't come on. Should I still go ahead with the other test?
I hear the actuator on the transfer case function, I'm pretty sure the problem is coming from the front driveshaft somewhere. I was thinking it could possibly be the celonoids for the a.d.d, not sure how to test it, maybe check the vacuum line?

 

Oh yours probably looks different because you have a vacuum operated ADD actuator, as opposed to the electrical one like on mine. In that case, I am not sure if all the tests can be done or will yield the same kind of results as they did for me. I would say they are worth trying though, as none take much time at all.

If you do indeed have a vacuum ADD, the first thing you should do is inspect all hoses, if you have not already. Mine has hoses, for venting, but not for actuation.

It may be different on yours, since you don't seem to have an electrical ADD, but on mine, there is a 4WD fuse in the cab. Make sure that's still good. As for the ADD solenoid, I wouldn't assume it's bad, but if you wanna test it, I recall it being under the hood on the passenger side, somewhere by the wheelwell. I am sure a little research could show you where exactly, and how to test it.

It still sounds like it is the ADD actuator from what you're saying. It's also the weakest link in the entire 4x4 system, and seems to be the most common part to go. Perhaps someone with more experience in this, specifically with vacuum ADD actuators, could chime in.

 

Sounds good, I will go ahead with the other test and see how it goes. I'm going to pick up a vacuum tester to check the hoses. I probably won't have a chance to work on it during the holidays but I will post back with some results. Thanks again for your help

 

A vacuum tester is a great idea. If you can get one to apply vacuum, perhaps you could hook it up to the supply hose for the ADD actuator and see if a direct vacuum gets it to function. If not, it would seem pretty clear to me that it is the faulty bit.

 

So here's where I'm at. I have replaced the add actuator with no change in symptoms. I tested the vacuum at the actuator and had vacuum on only 1 of the lines and the result didn't change with or w/o the 4x4 button pressed in. I then test the solenoids by jumping them with 12v and they both work fine. My next test is the relay. The Haynes manual says that it's in the passenger side footwell but mine is not located there. Any know of another place the a.d.d relay may be on a 99 tacoma?

 

Push button 4WD does not use a separate relay to control the ADD VSVs. They are are switched directly from the "4WD ECU". Haynes is near worthless for this kind of thing.
FWIW the vacuum ADD actuator in itself is very reliable compared to the electric version, especially when combined with the manual t-case.

Note that both/all the ADD systems will not initiate until the t-case 4WD "condition" or "confirmation" switch has made contact and is not stuck.

 

Thanks, I'll quit looking for the relay.

 

On top of transfer case actuator there is a "switch" with a 2 wire plug going to it. This tells the 4x4 ecu that the transfer case is engaged. Until this switch is activated the add will not engage as everything is controlled by a little computer behind drivers side kick panel.


If your vsv doesn't activate (check by taking hose off add actuator side and making sure theres vacuum. Youl hear it.) its more than likely that switch or computer itself.

 

Try and check the actuator on the transfer case, mines had a little water and gear oil in it. cleaned it up and it worked like a charm.

 

My transfer case works fine. I can hear the transfer case actuator work and the front drive shaft locks in. The problem is that the front excel doesn't engage with the drive shaft.

 

Start with the "4WD" switch (continuity in 4WD) then check for 12v power and operation of the 2 ADD VSVs, in and out of 4WD.

 

Transfer case in pic doesn't look familiar to me. But the switchs look similar.

 

Thanks, I'll do some investigating this weekend.

 

Pull the 4wd switch/sensor out of the front diff, and then test it with a multi-meter set on Ohms. Put the positive lead on one pin in the switch, and the negative on the other pin, and then try to hold them on the pins while pushing down on the switch to depress the round ball all the way in. If it gives you a tone reading each time indicating continuity, then the switch is good. If it doesn't then that switch needs to be replaced. It should be really close to the same setup as my 99 4Runner Limited 4x4 that I had, and I created the troubleshooting of the 4wd system of it on Yotatech.com

 

I just had a similar issue on my 02. The symptom was nearly identical with the trans case actuating, front driveshaft spinning, but no signal to the front diff to engage and thus no light on the dash. Turned out it was a wiring short in the 2 wire circuit devinzz1 mentioned in post #10 above. Mine had broken off inside the harness about 3 inches from the connector on top on the trans case. Patched it up and good to go.

Now my rear diff lock dash light blinks when I try to activate it and I get no sound or movement at the diff. Fun fun...

 

Sorry to revive an old thread, I think there is some very good info here but I have a few questions as I am having the same problem.

I have a 99 TRD with Vacuum operated actuator and ADD (but there is an electrical connection on the actuator the FSM calls it "ADD Switch Connector"). I also do not have the one touch 2-4 selector, I have the J stick (therefore there is no electric actuator on the transfer case). My 4x4 was working fine maybe a month or 2 ago, but the other day I decided to put it in 4wd just to keep everything working but I did not get any lights coming on, on the dash. upon further inspection I found out that the front drive shaft was in fact turning.

I have been reading this thread along with many others and I think my know my next course of action but I do not know how to do it. I want to test all 3 of the position switches on the transfer case (4wd position switch, L4 position switch, and neutral position switch), does anyone know how to test this with a multimeter? I also plan on testing the 2 vacuum lines on the front diff actuator, as well as the ADD Switch Connector on the front diff. Does anyone know how to test this connection with a multimeter as well?

Finally, I am not sure if this has anything to do with my problem but since I bought the truck I was never able to engage the rear diff lock. I have not been able to look into this problem very much as I have other things I am fixing. but I have tested for continuity at the 4wd ECU in the drivers kick panel and that tested fine. I am beginning to suspect that these 2 problems might be connected.

Any help would be appreciated.

 

RR will only work in 4lo unless you do the grey wire mod.

 

Yes I know this, rr diff lock did not work when my 4wd DID work.