My wife has a 97 limited with a 3.4, automatic, RR diff and 140K miles on it. The truck has been extremely dependable, and the 4wd has always worked until recently. Last week, I went to egage the 4wd (button on the xfer case shifter) and nothing. No light on the dash, no clunk under the truck and definitely no 4wd. The truck was going to the dealer for a rear axle seal change so I asked them to take a quick look. they told us that the 4wd was working, but the switch in the xfer case that triggers the light was bad. Needless to say, I respected the dealer a lot more before they told me this because the 4wd was NOT working at all. I can free-spin the front drive shaft when it is in 4wd and in drive (with the e-brake on and the wheels chalked), which tells me the front ADD isn't engaging either. I swapped the hoses on the vaccum solenoids for the ADD, and it engaged, but not at the xfer case. I read out the switch on the shifter from the 4wd computer (in the drivers kick panel) to ground, and the switch was working fine, so I replaced the 4wd computer. Now I'm out $100+ for a computer, and it still won't engage in 4wd (anyone need a 4wd computer ???). I've searched the threads and only found one other person with this problem, but no answers.

ANYONE?
PLEASE?


Bueller???

 

OK we got 4wd issues in 3 seperate threads now.

......I posted in here:
https://www.yotatech.com/forums/show...1#post50355271

Sometimes you can also use a hand actuated vacuum pump (it's better if you can get one with a guage attached.....otherwise you should tee off a vacuum guage to make sure you don't apply too much vacuum and damage the vacuum diaphragm) to force the diff into 4wd (just to verify it is a vacuum issue). Once you have this nailed down it is easier to just focus on why you are not getting vacuum when the vehicle is put into 4WD.

 

I will try that tomorrow (once I get a vac pump). I just took another look, and here is exactly what is happening (or not happening!). With the engine running, in park, I push the 4wd button and no response. The red vaccum solenoid remains energized... that is, when I pull off the hose to the ADD, I hear the vaccum (at this time, I can free-spin the front drive shaft). When I pull off the blue hose, there is no vaccum. If I push the 4wd button (disengage), the vaccum remains on the red solenoid. At no time was a vaccum present at the actuator on the xfer case or on the ADD side of the blue vaccum solenoid. I traced that vaccum line from the xfer case actuator, and it seems to go back into the xfer case on the top side near the front of the xfer case. All hoses had a good seal. I guess my next question is where does the vaccum for the xfer case actuator originate? I couldn't easily find it from beneath or above the engine. I should also mention that when I swapped the ADD-side hoses on the vaccum solenoids, the ADD engages (I could not free-spin the front driveshaft), but no 4x4 light came on. I verified that it was not in 4WD by flooring it in the grass and only the rear wheels spun. Does the ADD engage only once the xfer case has engaged? Where does the vaccum for the xfer case come from? Other than the switch and the 4wd computer, are there any other components (other than a vaccum) that are common to the xfer case and ADD? If whale oil comes from whales, vegetable oil comes from vegetables, mineral oil comes from minerals, corn oil comes from corn and olive oil comes from olives... where does baby oil come from???

I need answers!

 

Okay, here is the latest...

To improvise a vaccum pump, I ran a vacuum line from the triple-T by the vaccum switching solenoids, in place of the vaccum reservoir, to the actuator on the xfer case. With the engine running and the button pushed, NOTHING. WIth that setup, I then swapped the ADD side vaccum hoses on the solenoids, and the ADD engaged, but still no xfer case. Has anyone experienced this? I'm thinking at this point that it might be the xfer case actuator, but that doesn't explain to me why the vaccum switching solenoids aren't switching either.

ANY AND ALL HELP IS APPRECIATED!!!

 

It's hard to explain exactly what's going on in your ADD system, if you get the Toyota Servce manual it has all the diagrams. On your Transfer case is an electric motor that switches in your 4wd. It could be the actuator hanging up or any one of the systems connected to it. In the Factory service manual it has a trouble shooting diagram to follow, this will narrow down the exact problem.

 

Can be a number of things. Is it "select shift" or not? VSV's for servo vacuum. ALso, there is a rleay on the pass side that can fail and not allow 4WD. I have actually seen that on a 97 4Runner first hand. I fthe vacuum hoses were on the servo backwards, it would show a green 4WD light momentarily

 

Thanks for the ideas!

Where is the best (cheapest) place to get a service manual?

Where on the passenger side is this relay (I've read about it, but could not find it)?

 

I'm experiencing similar problems. I have even gone so far as to swap out the vsv (under the fuse box). MDT Tech, in you post you mention a relay, where exactly is it located? thanks...

 

I've had a similar problem with my rig. The problem is intermittent so that makes troubleshooting even harder. I've narrowed it down to the electronic motor in the t-case. With ignition on but engine off you should be able to hear the electronic motor operate when the 4WD button is pressed (both engaging and disengaging). If you hear nothing then you have a problem. Mine misbehaves in cold weather (when I least want to work on it) but works ok most of the time. I've cleaned all the obvious electrical connections. Fortunately, it doesn't get cold here very often but one these days my laziness to fix the problem is going to strand me...

 

Where exactly is the ADD unit located? I usually have the opposite problem. Mine won't come OUT of 4wd. lol Anyone have pictures or a good description of where the ADD unit is located on our vehicles?

 

From what I understand, the ADD is IN the front axle (AUtomaticall Disengaging Differential). It is vaccum operated, with the two vaccum switching valves (VSV's) located on the drivers-side wheel well under the hood. One valve is blue and one is reddish brown. These valves either engage or disengage the front differential. I verified my ADD is good by swapping the vaccum hoses. With them swapped (and the engine running) I cannot turn my fron drive shaft (Wheels are engaged). If you engage it this way, it will remain engaged until the vaccum is applied to the other side (swap the vaccum lines back).

I was afraid I'd have to tear in to the xfer case. But first, I'm hoping someone can tell me where this relay is located on the passenger side first...


ANYONE?!?

 

MDT!!!! where is the relaaaaaayyyyyyyyyyy?????

 

This is for a Tacoma, but it should be very similar:
http://www.deserted1.com/FSM/Repair_...y14wd/loca.pdf

 

Thanks!!!

That is a good start, however, I have to ask if that is an electronic service manual you linked? If so, how do I get one???

 

A quick follow-up;

I troubleshot as much as I could and ended up thinking it was the shift solenoid in the xfer case. A reputable dealer confirmed it and almost $1300.00 later, I have 4x4 again. The syptoms were not the typical symptoms that you read about. When the 4x4 button was pushed (on the xfer case shifter) nothing happened. No light flashing, no cl-clunk underneath, nothing. the only thing lost here was time, but I'm hoping this will help someone down the road.

BTW, the cost for the solenoid itself was over $800, so if you are experiencing this particular problem, be preparred to shell out some $$$!

 

Ouch! Thats some serious coin. From the FSM it looks as though you have to disassemble the t-case to get the solenoid out. Is that the case? You have the old solenoid to snap a few pics of? I'm wondering how difficult it would be to convert the thing to full manual and get rid of the troublesome solenoid system.

 

You are correct about dismantling the xfer case, and unfortunately I don't have the old solenoid anymore. But I have to admit, in 146812 miles, this is the first pricey repair we've had to pay for. That's not too shabby, and in truth, it didn't affect our daily driving.