Hi!
I am a 17 year old who drives a 1999 4runner limited.
I believe I am having a similar issue and I would love to talk to you about your experience to see if you would be willing to give me some tips. Thank you!

 

Just a note on all this: Something to help keep the electrical connectors of safe from corrosion, dirt intrusion, and so on, is a dab of silicon dielectric grease in them. Quick, easy way to keep them safe. Just climb under there, pop each connector loose, one at a time, squirt a dab of the grease into the female side, and put them back together again. It may sound like a no brainer, but so many people ignore the connector portion of the sensors (switches), which can get dirt, water, etc, in them so easily. The seals on the connectors get old, and start to leak like sieves, so a little dab of the silicon dielectric does wonders to protect them.

Just a thought...

Good luck!
Pat ☺

 

where is the front diff sensor located?

 

On the ADD locker, upper section, towords the passenger side (the right). Remove the slider, it will make life So much easier. Follow the electric connector up from where it connects into the wire bundle in the area. Unplug it from the wire bundle, and, if you can, you'll slip a 27mm box wrench up along the cable. The switch (sensor) will unscrew from the ADD case easily, once you break it loose. It might be a little difficult to break loose initially, but once you do, it unscrews easily.

Do not be alarmed by a small amount of differential oil that may leak out. It's a bit messy, but won't hurt anything.

Presuming it's a 2 wire connector, place a lead from each side of the multimeter, one red, one black, put the multimeter into the lowest ohm reading it has, and check the switch. It should read infinity when the plunger is extended, and 0 ohms (or thereabouts) when it's compressed all the way into it's case. If it fails either reading, it's bad, and needs to be replaced.
The torque on the switch, according to the pictures above, is 27ft/lbs.

Does all that babbling help any?
Pat☺

 

Thank you so much! It definitely does a little. Follow up questions, just to clarify, the front differential sensor is located on the transfer case? Which sensor is it in the attached image? Also, are there any other sensors near it I need to worry about? The one you described is for 84222-35070? What slider do I need to remove? Can I manually adjust the plunger to test it once I have it removed?
Sorry to ask so many questions, I just want to make sure I know what I am getting into. Finally, and most importantly, is this able to be done by a beginner mechanic like myself. I don't want to make the problem worse. Thank you!

 

Is this the sensor on the back of the front differential? Part 84222-35070 and code 84222C?

 

What slider to remove? The one that covers the front differential, and the ADD system. IIRC, it has 4, 12mm bolts holding it on. Just a flat plate of metal, protecting the front differential, ADD system, front drive shafts, and so forth. I use a jack of some sort, or even a jack stand, to hold it in place, rather than trying to push it up with my arm strength, which isn't what it once was. When installing it, you'll need some way of keeping it close enough to the bolt holes to at least get them started.

No, the sensor is not on the transfer case. It is on the ADD case.
Once you get the sensor removed, you can manually push the plunger in to test the sensor. Sort of like pushing in the plunger on a syringe. All the way in, 0 ohms. All the way out, in other words just sittin as though it is fresh out of the package, untouched by human hands, infinity ohms. Actually, it doesn't have to be very far out of "all the way in" to go from 0 ohms to infinity ohms. It's just a switch. Open/closed. Open, infinity ohms, closed, 0 ohms. plunger in, closed. Plunger out, open.

Does that answer your questions?
Pat☺

 

Perfect for the information about testing. Thank you. I'll take a look here

 

Hello, I recently purchased a '99 Limited 4runner with a rear locker. I knew it had problems with 4wd when I bought it but it has low miles (126K) and it had not rust so I went ahead with the purchase. Mistake? I hope not. The issue, I thought, was that since the indicator lights on the dash were not lighting up 4wd was not engaging. However, since purchasing i have found the story to be more convoluted. When i press the "4WD" button on the transfer case shifter nothing happens. No lights, no audible mechanical engagement. When I pull the shifter back to what should be 4H locked still no lights and no audible mechanical engagement. There is also not a very clear sense of the shifter dropping into place when I go into 4H locked. It feels very ambiguous. When I shift to 4L it feels solid and there is a clear change in gearing. When I engage the rear diff lock I can hear the actuator engage and the rear diff lock indicator on the dash lights up. Duribg all of this however, the four little green wheels and the little orange center never light up at all.The thing I most recently discovered that really has me
confused is that when I try to turn the front driveshaft it appears ti be engaged as it will not turn. I just picked up a second set of jack stands so that I can get all four wheels in the air and confirm what is actually spinning when the truck is in drive and what, if anything, is happening when I shift the transfer case and lock the rear diff. I have the Toyota shop manuals and I have watched and read everything I can find to educate myself. I have had eyes on all the actuators and switches. I have seen that the A.D.D. system vacuum actuators look pretty beat up. The filters are missing and it looks like someone may have messed with the vacuum lines so that was one of the first areas I had intended to check. I have posted on two other forum but had no replies. I'm feeling a bit overwhelmed. Any help would really be appreciated. Thanks

 

I don't have my '99 any more but I do remember that you can apply 12V to the 4WD actuator on the transfer case manually and manipulate it in both directions. I had to do that to get mine out of 4WD a couple times before I got it fixed. Good way to prove the actuator is good too. It is odd to me that you are getting no "wheel" indicator lights at all. Whenever I had problems they always just blinked forever. It seems like it would be a strange failure but I would be sure that 4WD button/switch is good and the continuity is getting to wherever it needs to go. I loved my 99 limited. I hope you can get yours working right. Keep the leather treated and supple if it's still good. I failed there.

 

I did check the continuity on my selector button and it was good. I am going to order some bulbs and pull the instrument cluster. The bulb for the “D” on the gear indicator section is burnt out also so it needs to be done anyway. I’d like to do all LEDs but I’m going wait on spending that money till I get the 4wd system working properly. I’m wondering if the 4wd indicator lights were blinking so long they burnt out. I still need to check all the switches for continuity as I’m pretty sure I have a problem there as well. Can anyone let me know if their 4wd drive indicators light up briefly when turn on the ignition? My rear diff lock indicator lights up but me 4wd indicators do not. Thanks

 

I would bet the little bulb(S) for the 4WD indicator are burned out. Mine don't turn on when I first turn the key on, IIRC.

I would also bet that it's the actuator that's your problem. The grease they use get's old, especially if the PO didn't exercise the 4WD regularly, and/or the traces get worn. Pull the back off of it and look. Chances are, it just needs a real good cleaning with some good quality electrical contact cleaner. Spray it in, give it a good scrub out with a moderately soft brush (old, worn out, toothbrush works great). Keep spraying while you scrub to flush the crud and old grease out. Once ALL the old grease is gone, put fresh silicone dielectric grease all over the board the wipers ride on. Not a lot, just a thin layer. Put it all back together, and test your 4WD.
If I understand correctly, when you engage your 4WD, the front drive shaft doesn't turn freely any more. That tells me the ADD and transfer case are both working correctly, but I may be wrong on that.

It might also be a good idea to test the switches on the transmission. There are 3 (on my manual tranny), and it doesn't take much for them to get intermittent. Sometimes they get to where they make either just after the actuator that makes them switch pushes them all the way in, or just before. Either way, they don't operate properly. You can check them fairy easily. Hook a multimeter across the pins on their plugs, there's only two, and polarity doesn't matter, and press the plunger in until it's flat to the case. Check the multimeter as you push it slowly in, aand look for where it makes, if it does. Make sure the plug is clean, too. No grease or other crud inside.

IMHO, your focus on the diff locker is misplaced. It's for the rear diff only, and doesn't engage unless you're in 4 low, and under a certain, very low speed. I think 5 MPH, but I may be wrong on that. Point is, it really doesn't enter into worry about the 4HI engaging at all. Nor does it affect the front differential.

Good luck!
Pat☺

 

Hello all, I am still trying to figure out my 4wd indicator light issues. Not actually even sure I have one to be honest. Can’t anyone with a 99-00 Limited tell me if their 4wd indicator lights light up when you first turn the key in during the brief system test? I have pulled my cluster and managed to check the bulbs and they appear to be okay but they are honestly so small it’s hard to be sure. Especially for old eyes. While I am asking has anyone experienced or even heard of someone experiencing those bulbs going out? And, does anyone know what size the are? They are. Clearly smaller than the rest of the cluster bulbs which I believe are T5?

Thanks for any help )

 

I have had the 4Runner up in the air and confirmed my suspicion that the transfer case has been stuck in 4wd. I hope not with the center diff locked. Im think not because there have been no horrible noises. I also managed to pull and test the #1& #2 4wd switches. Both expressed continuity although there was a break momentary break during full travel. Hard to describe so I won’t try. Anyway, they seemed okay from what information I’ve been able to get. Still need to check the rest of the switches but that will be tomorrow. I was able to jump the transfer case actuator and get the transfer case out of 4wd but in the process the actuator seemed to give out as further attempts to jump it got nada. I addressed the vacuum solenoids for the front diff actuator and found that someone had disconnected the vacuum line that connects the blue solenoid to the brown solenoid and plugged the line with a bolt leaving the brown solenoid open to the wind. I reconnected it but nothing changed. I will get to checking the front diff actuator vacuum and the switch tomorrow along with checking the rest of the other switches. I’m going to source a replacement transfer case actuator cuz even if I could get it to work I feel that it will continue to be a weak link. I have ordered what I hope are the correct bulbs for the gauge cluster 4wd indicator lights. They should be here tomorrow. I figured for $10 I’d just replace them and eliminate that question. To end on a positive note, I was able to confirm that the rear diff lock actuator works perfectly so yea for that. As always, to anyone who has wisdom and the mercy to share it please feel free to do so. Thanks

 

Just in case anyone might happen across this thread. I have found the answer to the question of why I have had not 4wd indicator lights. I chanced across a video in YouTube that showed where the 4wd control unit was located. I had assumed that I’d have to hunt for them from the way they are pictured in the Toyota shop manual but didn’t realize they were right behind the driver’s side kick panel. When I pull the kick panel I was surprised to find that someone had unplugged the “4WD Control Computer” (part# 89533-35150). It immediately occurred to me that this had been done to address a problem that whoever unplugged the module to solve a problem that this person couldn’t or didn’t know how to fix correctly. I was concerned that something would may go wrong if I plugged it back in but I figured I’d never know if I didn’t so I did. Bingo, flashing 4wd indicator lights. Lights that would not go solid or turn off. This was not surprising as I had previously checked the A.D.D. switch and found that while it would kind of make continuity it was without question wonky. And there still remains the matter of diagnosing the vacuum system. With the lights active I was able to confirm that when I press the 4WD switch in the transfer case shifter the lights briefly for solid but then go right back to flashing. It seemed that the system recognized when I moved the shifter to H4L but I couldn’t be as certain. The thing that went wrong when I plugged in the 4wd ECU was that the transfer case actuator, which I had thought died on me the night before, went live and dropped the transfer case back into 4wd. I tried to jump it back into 2wd and it seemed to be actuating but it would not go back to 2wd. All of this would actually have been a positive save for one glaring issue. Right about the time that I tried to get the transfer case back to 2wd the transmission started making a whirring noise and then started making a clicking noise when I tried to put it into Park. Now it sits in my garage immobile as it will not engage and drive the rear wheels. I am defeated

 

In the post above I mentioned that I had found the “4WD Control Computer”(part# 89533-35150) what I didn’t mention was that I also found a second “4WD Control Computer”(part#s 89533-35070/ 179600-0201). I have attached pics for reference. I the shop manuals I thought I only saw one 4wd ECU. Can anyone shed any light on this for me. Please

 

If I am understanding correctly when I run the above part numbers through the Toyota parts website 89533-35150 is the main 4wd control computer and the second 4wd control module, part# 89533-35070, is a sort of piggyback that is added when the truck is optioned with a locking rear diff. I had seen or heard that there was a relay but that must Mary depending on year and model

 

I do have a spare 4WD Computer and (1) brand new Toyota 4WD sensor switch for the transfer case.

I have a 97 SR5 4Runner 4x4 now, so I won't be using those parts at all.

The brown VSV to the front ADD is for 2WD mode, and the blue VSV is for 4WD mode.

Verify that the vacuum lines to the VSV's are correctly routed to each one from the ADD, otherwise your 4WD and 2WD will not work correctly at the ADD.

 

@99SC4Runner Thanks very much for hitting me back. I have finished checking the vacuum solenoids, vacuum lines and the A.D.D. If my diagnostic ability is worth the time it takes to type it out here is where I’m at.

The vaccum lines all appear to hold vacuum fine. The solenoids are toast I believe. When I ran power to the brown solenoid it sounded like it was moving air a couple of times in one polarity and then only clicks. The blue solenoid just clicks. I believe that means they are no good? I came across a thread when it was pointed out that although for 4Runners there is just one part# for the solenoids there are individual part#s for to their vehicles similar vintage that use the same solenoids. I have ordered them new on Amazon and they arrive tomorrow.

A.D.D. Actuator seems to hold vacuum well in one port but seems to have a very slow leak. I am not certain about that though because the crappy vacuum tester I have is also suspect. My question is should the actuator hold vacuum indefinitely? It seems that it should but the shop manual does not specify and I have no experience with this unfortunately. I plan to order a new from Toyota along with the A.D.D. switch that I also pretty certain is bad.

I believe my transfer case actuator is also dodgy. The motor works a couple of times in succession then quits for the night. I’m pretty sure that isn’t correct? Because I question everything I do I’ve checked it several times and it’s always the same. Works a bit then doesn’t until the next day. In my limited experience that is an indicator that the motor is toast. Which I found surprising as it looks very healthy. I did have a question as to whether or not the shaft for the rotating gear should have a bearing in the cap? It looks like it should but mine does not. Anyway, I can’t seem to find a used actuator only transfer cases but since a used transfer case is $300 locally versus $1200 for a new one from Toyota I’ll be going that route

I believe that my 4wd #1 & #2 switches are good but plan to double check them when I finally get to checking the 4Low, Neutral and Center diff lock indicator switches which will hopefully happen tonight.

@99SC4Runner do you know what activates the center diff lock? I have been told it is mechanical and I have been told that it is a switch that is activated when putting the transfer case shifter in H4L. I am currently believing that it is the latter. However, I am uncertain as to which switch handles that function. I have also seen the shop manual refer to a “limit switch” but as I don’t see a switch with that title I assume the task is handled by one of the other switches?

Thanks for any help, Mario

 

The vacuum diaphragm in the ADD should hold air in both directions, and not have any bleed down. If it can't continuously hold air pressure, then the diaphragm is leaking and should be replaced.

If you can jumper the transfer case actuator with 12v, it should move the actuator into 4wd mode, and then alternate it back into 2wd mode. With a constant 12v to test with, and if it moves the actuator each time with 12v, then the actuator is good.

A known good used transfer case is much cheaper and easier to swap out then splitting the transfer case to just change out the transfer case actuator.

The center diff lock activates once the 4wd system knows that the transfer case and the front diff are both in 4wd mode, via the front diff and center diff lock sensor/switches providing feedback to the 4wd computer.

The center diff lock is a single switch/sensor on the passenger side of the transfer case (single sensor on that side). I do have a brand-new Toyota sensor for it still sealed in the bag for sale. Also, I have a spare 4WD ECU computer for sale as well.