SigEp4Runner

Ive searched all over and found some information on the site about trouble shooting, but my problem seems to be different than other threads.

This picture is from one of the other threads and it says:
"In the picture there are 2 cellenoids.
THe Blue one is the ADD off, And has power when the transfercase is in 2H and cause a vacuum at one of the hoses at the diff.
The Blue one turns off when the put into 4H/L
The Red one is ADD on and has power when the T-case is in 4H/L and will cause a vacuum in the other hose at the diff.
The red one is normaly off when in 2H."

I checked these hoses on my rig and the red one is always getting vacuum and the blue one isnt. This happens if im in 2h or 4h/l. My 4wd doesnt work and the light doesnt come on. I also tried switching the hoses around to see if it would engage the 4wd, but still no light on the dash. Is this an electrical problem? How can I go about fixing this?

Any advice is helpful. I may give a buddy a call that might be able to troubleshoot further, but this site usually gets the problem fixed faster.

Oops just noticed i wrote "ingaging" instead of engaging.

toyota4x4907

I had the same problem when I bought my '95 4runner. My problem was the diaphragm on the ADD modulator on the front diff was stuck. I had to pull that sucker off to find out what the problem was. Its really easy. 4 bolts, some silicone sealant and some diff fluid. After I did that, I locked the two shafts together permanently since I already had manual locking hubs. Most likely you will have to REPLACE the whole modulator because even though I freed the diaphragm up, it still wouldnt be moved by vacuum.

runnermedic

check the diff actuator plug all the way.
maybe is working but the light not.
there is a connector near the oil stick is the actuator indicator mine was dirty and the light wasnt working but the 4x4 where working.
good luck!!!

SigEp4Runner

Thanks for the reply, i just searched ADD Modulator and found your other reply to gsull here https://www.yotatech.com/forums/f116...ge-4x4-192457/

I'll try following those steps when I get the chance.

As far as the diff actuator plug, I know my 4x4 isnt working because I've been stuck to the point where my rear wheels were spinning, but the fronts werent engaging at all.

thook

If you're not getting vacuum on the specified cellenoid when in 4wd, that would indicate to me an issue prior to the actuator in the system. Namely the switch at the t-case that signals the 4wd cellenoid.

Not sure where the t-case switch is, but it may be in the online FSM under transfer case. I'd have to look under my rig to find, but it's at home...........and, I'm at work.

SigEp4Runner

I was thinking the same thing and I'm concerned because the wrong solenoid is getting vacuum all the time. Is this similar to your situation toyota4x4907?

thook

I didn't find any pertinent images in the FSM posted from this forum. Not surprised..........there's a lot that's been left out of that copy.

Hmmmmmmm.......maybe 4runnerX3 has something. Otherwise, I can't help anymore until tomorrow.

SigEp4Runner

I think there is just too much that this could be. Im gonna print off the info you guys have given me and this trouble shooting page I foundhttp://personal.utulsa.edu/~nathan-b...26addcontr.pdf and go to my buddy. He does a lot of my work that I'm not comfortable doing. He rebuilt my transmission for me and that is when the 4wd stopped working so maybe he hooked something up wrong. I'll post the results later this week after we figure it out.

SigEp4Runner

So looking at the link i just posted i found that the red solenoid in the picture i first posted is the 2wd one (VSV2). Thats a relief i guess. In the diagram it shows a fuse, but my owners manual didnt specify a fuse for 4wd. Is there a fuse that I should check for this system?

SigEp4Runner

So it took a lil longer than expected because my buddy has been pretty busy so I decided to take a look around while I was visiting my dad this weekend. He has a large work shop so I parked my rig inside and got it up on four jack stands. I then got under the car and had my dad use an antenna as a pointer to trace the vacuum lines from the solenoids down to under the engine so I could see from underneath the car which ones I needed to look at. I took the skid plate off in order to see the front side of the front differential where the lines lead to.

Here is a diagram of what I was looking at. The red square shows the actuator that engages the 4wd, this is where the problem was.


View of vacuum lines at the solenoids:


Here is where the lines come out underneath the engine right in front of the front differential behind the skid plate:


And here is where the vacuum lines hook into the actuator:


These lines going into the actuator looked pretty dirty so I disconnected them one at a time, making sure not to hook them up wrong, and cleaned them real well. After I connected them again the 4wd worked like a charm.

Now there could be many other problems with the 4wd system, I am happy mine was so easy to fix. This may not fix everyones problem, but this is a good place to start the trouble shooting so I thought I would share the info.

2DoorRunner

Thanks, i plan on doing the same thing in the next few days, and you just made my job alot easier.

SigEp4Runner

No problem 2door. I may not have the best knowledge about working on our rigs, but when I fix something I like to post it because it may help someone the same way that this site has helped me. Good luck with yours 2door. Thanks for all the help guys!

Jeremy11

Check your vacuum lines going towards the intake. ?I had the same problem and the hoses were going to the wrong spots therefor not getting any vacuum to pull the slip over to connect the axle and front differential. If the light doesnt turn on either its more than likely your problem. Here id the diagram

Just follow the diagram and it should work. The first hose on the top set of 3 iinserts i put the hose coming out the little circle thing cominf from your vacuum pump. the circle thing runs to the right of the ADD cellonoids.

Hope this helps.

jkdunbar

Hello All,

I have the same problem and I'm trying to troubleshoot. So my first question: If I take off the vacuum lines that are circled (from the vacuum canister split into two) while the truck is running, should I have vacuum pressure?

Presently I do not...

SigEp4Runner

Yes there should be vaccum in one of the vacuum Solenoids while the vehicle is on. The red one is the 2wd and the blue one is 4wd. There are a few threads I looked at about this, most people have holes in their vacuum lines feeding in to the solenoids or there is a vacuum tank in the passenger fender that goes out. Either one could be your issue along with other things. I'm not too framilier with the ADD components which is why I'm lucky my problem was so easy to fix, but i'm sure there is some one here that could help you out.

jkdunbar

Got mine working. It was the vacuum lines.

FYI - test the 4WD line by connecting it directly to the main vacuum line coming out of the engine. If your 4WD light come on and it engages, then it's a vacuum line somewhere and just replace them all one at a time.

Jerbou71

Ok guys my 4wd isn't working ether, so the first thing I did was check the vacum and it is good at the cellenoids. The thing is when the truck is on if I put it in 4h the shifter lock in place but if I put it in 4L it won't stay there it slides back to the 4H postion. I took off the actuator and put vacum to it and it works back and forth no problum. I have been getting parts of a 91 4wd and there is no battery in it and when I try to put it into 4h and 4L it does the same thing, so I was wondering if on mine the 4wd system is just not getting electrical power to work. Any ideas?

Jerbou71

Anyone?

SigEp4Runner

I dont know a whole lot about this stuff, that is why this forum is great, I just learn stuff as it goes wrong. As far as your problem goes Jerbou, it sounds more like something in the tranny, if im right, the only difference between the 4hi and 4lo is the gearing not the actual locking of the front axle. The ADD system only takes care of locking the axle in place and the gearing from hi to lo is all from the transmission or the transfer case I believe? My transmission slips out of 1st gear sometimes so maybe this is similar to your problem.

Again I am not too knowledgeable with this stuff so I could be completely wrong. Hopefully someone else can help with a bit more knowledge

bobo jones

when i engage my 4 wheel drive i hear a click from my dash but the light doesnt come on and im pretty sure its working whats the easiest way to tell the 4 wheel drive is working. any help is greatful thanks