I've got a 99 4Runner LTD V6 with auto trans and it has the M/M - 4WD style shifter in the transfer case.

One day last week I decided to use the M/M button instead of manually shifting the lever into 4HI, and when I did the 4WD light on the dash blinks. I tried shifting it back into 2HI and the light still blinks all the time. I jacked up the 4Runner on jackstands and it is in fact in 4WD mode and I could feel it when I had to drive on dry pavement with the front end still being engaged in 4WD. One rear tire was spinning and both front tires were spinning for a while, but then it was just the left front and rear tire spinning up in the air.

I jumpered the rear transfer case actuator with 12v on pins 2 & 3 and then reversed the polarity to run the actuator into 4WD and then back into 2WD mode. I did this several times. It worked like it should back and forth without any problems. I decided to put into 2WD mode on the rear actuator and then start up the 4Runner. The light was out and I could tell that I was in 2HI like it should be.

I tested the vacuum lines from the ADD solenoids to the front diff, and they both held 20# of vacuum and did not bleed down. I tested the line from the T to the vacuum canister in the left front wheelwell, and it held vacuum. I tested each line down at the front diff and both lines held 20# of vacuum, but I could not hear the collar in the front diff move either time. I tested the vacuum line from the intake down to the 1 way valve and it held vacuum as well.

Then I tested each ADD solenoid and the brown one had 37 ohms of resistance, and the blue one had 39 ohms of resistance. I read that they are supposed to have 38-45 ohms, so the brown valve is close to being within factory specs.

At this point since I cannot hear the collar move at the front diff actuator, I'm leaning towards it as the culprit or the brown VSV valve.

I swapped out the 4WD computer and it still is doing the same thing.

Here are the pictures;

 

I have the exact same problem on a 2000 LTD. Seems to be popping up more and more. The searches don't really help either. I'll be following your progress.

 

I'm leaning towards the front diff actuator being stuck since I can apply vacuum directly to each side of it and I don't hear the collar moving back and forth.

But I need to jumper the transfer case actuator back into 2HI mode and then jack up the front end and see if the axle shafts are still gonna turn.

I'm gonna test the ADD solenoids by jumpering power to them with the electrical connectors unplugged and apply vacuum to the lower hose I believe to see if it will exit out the top or not. Then I'll disconnect power from it and see if it will let the vacuum bleed down.

 

I got to do some testing of some of the sensors for the transfer case tonight and the actuator on the front diff.

I unplugged both vacuum lines off of the front diff and I applied vacuum to the driver's side line on the actuator and then I tried to turn the front driveshaft, and it wouldn't turn so it was acting like it was in 4WD. Then I switched and applied vacuum over on the passenger side vacuum line on the actuator and it allowed me to turn the front driveshaft by hand being it was in 2WD. At least that part is normal.

Then I removed the two sensors one at a time on the back of the transfer case above the rear actuator. I put my multimeter on continuity and then put both leads on each of the 2 pins on the sensor. With the sensor extended out, there was no circuit. Then when I pushed the button on the sensor in, it completed the circuit and gave me tone. I repeated the same thing on the other sensor on the back of the transfer case, and it did the same thing. So those appear to be normal.

I need to pull the 2 most forward sensors off of the left side of the transfer case near the top to check them yet. Also, I need to do the same for the sensor on the front diff by the actuator to test it.

I can manually shift the transfer case lever, or push the M/M button and get it to go into 4WD mode (and it is from my previous test), but when I shift it back into 2HI it will not disengage the front end. I've tested all the vacuum lines in the 4wd system and everything holds vacuum.

Here's my question.

If the front diff sensor is bad, it will not tell the computer that it is locked or unlocked, resulting in the system thinking that it is in AWD mode right? My 4wd light on the dash just blinks and never goes solid like it should if the front end tells the computer that it is locked in.

I already replaced the 4wd computer with another good one and that didn't change anything either.

I need to test the 2 ADD solenoids with a 12v and vacuum test done on them and verify that they are in working order. I have to buy a sensor socket or a stubby end wrench to remove the 2 more forward sensors at the top of the transfer case and the front diff sensor yet so I can test them like I tested the first 2 tonight.



Thanks,
Doug

 

Wow Doug..thanks for keeping us updated on your research. I really appreciate it. I hope you track it down! It's strange that I have the exact same problem as you. I wish i knew more about my 4wd system so I could help you. Unfortunately i have some other serious problems with my truck thats been keeping me busy but thats in another thread.

 

Here's an update from some troubleshooting that I just did.

First off, I had to shift the t-case into 4HI this morning as I had 8 inches of new snow to drive to work in. The 4wd light on the dash just started blinking and would not totally lock up into 4wd mode, but you can feel the front end is engaged. Then at lunch time I had to run into town for some supplies for work and the roads had thawed out enough to not use 4wd, so I shifted the t-case lever back into 2HI, but the 4wd light was still blinking like it has done for the last few weeks. I went to Walmart to get the supplies and shut off the 4runner. When I came back out and started the 4runner, the light went out on its own and I was in 2wd mode for real this time. So then I was thinking WTF is going on with this thing? I went home after work and the roads were a little bit icy so i pulled my t-case lever into 4HI and the lights blinked for a couple times and then went solid and showed that the 4wd system was indeed locked into 4x4 mode. I shifted it back into 2HI and it disengaged the front end and I was in 2wd mode. I was like well isn't that strange? It's working again. While I was in 2HI I pushed the M/M button in and it blinked a few times and then it went solid with only the 4 lights resembling the 4 tires of the 4runner being lit. So now M/M was working correctly again also. Hmmm? Even though it was working, I decided to check the last 3 sensors for the 4wd system to determine which one is causing the problem.

So I bought a 1 1/16" end wrench and I took a grinder and cut the wrench into 2 pieces, the box end has about 4" of wrench attached to it, and the rest is on the open end side. There are 2 sensors towards the top of the t-case on the driver's side - Front one is BLUE, and the Rear one is GREEN. I took the box end wrench piece and I put it over the green sheathed sensor and used a pry bar to pry up on the bottom side of the wrench to break loose the sensor. BE VERY CAREFUL OF THE VACUUM LINE AND THE WIRING HARNESS THAT RUNS ALONG BY THE SENSORS SO YOU DON'T DAMAGE THEM! I removed that sensor and used a continuity check on the Multimeter by putting both leads from the meter on to each pin on the pigtail, then I pushed down on the button of the switch and it gave me an electrical readout. Then I removed the front blue sheathed sensor in the same way, and performed the same test to it. It gave me a similar readout on the multimeter. Then I installed the 2 sensors in the reverse order starting with the blue one and then the green one, and I tightened them down and plugged them back in. Then I removed the rear skidplate from the front end and I unplugged the sensor switch that is by the front diff actuator. I took the open end wrench piece that I cut the wrench from and broke loose the sensor. I removed it and used the Multimeter on it with each lead on both pins of the sensor and then I depressed the button on the sensor. It gave me NO continuity beep or an electrical readout on the Multimeter. I depressed it repeatedly with it only giving me a beep once in a while. So then I put it back together and I tested the 4wd system on the ice again. Now my 4wd dash light is blinking in 4HI mode and in 2HI mode again and the front diff will not disengage. It's now doing the same thing again as it has for the last few weeks.

So at this point in time, I'm at the conclusion that the front diff sensor is whacked out. If you think about it, it is the sensor that tells the 4wd computer that the front end is either locked into 4wd mode or unlocked into 2wd mode. It is also the sensor that truly tells you that your 4wd system is engaged or disengaged by giving you the light on the dash. The button on the sensor gets depressed when the front diff actuator goes into 4wd lock mode, and then it gets extended back out when the front diff gets disengaged from being shifted back into 2HI.

So I'm headed to Toyota in the morning to see if they have the front diff sensor, as I'm 95% sure it is the one that is messing up my 4wd system.

I'll keep you all updated when I get it installed and tested again.

 

Had the same problem with mine. I went into the dealership to buy the replacement one and they told me that the failure was so common they stock at least 6 of those front ADD type sensors at all times.

 

What's the part number for that sensor?

Thanks!

 

Okay fellow yota owners;

I went to Toyota today and they had to order both sensors that I wanted. I wanted the Center diff lock sensor which is on the passenger side of the transfer case, and the sensor for the front diff.

Here's the part # for the front diff sensor - 84222-35070 and I got it for $36.94.

You guys will be happy. The parts guy at Toyota let me look at the FSM for a 99 4Runner and he photocopied what pages I wanted out of it.

The "BLUE" ADD solenoid is your 4WD solenoid, and the "BROWN" ADD solenoid is your 2WD solenoid.

I got the wiring schematics for the 4wd system with the 2-4 select switch (M/M) transfer case, the exploded diagrams of the t-case, and the description page of what each sensor does. I'll get them scanned and posted in the thread so that all of you will have some good reference material for troubleshooting.

My local Toyota dealer said that they haven't seen any 4wd failures on the 3rd gen 4runners and the tacomas in my area. They said that they have ordered 2 front actuators for people but that was it.

 

Sweeeeet! I hope it's just that sensor. For $36 bucks i'll run out right now and buy one. I'm so sick of being stuck in 4wd. It makes for some pretty boring wheeling trips.

 

Sounds like we are going through the same thing. The wifes 2000 4Runner LTD 4x4 is stuck in 4WD mode. Exact same symptoms, blinking 4WD light. The stealership has replaced both t-case sensors and now they are telling us that the problem is with the actuator and they want $850 + labor to fix.

 

Make sure you test the transfer case rear actuator with like a battery charger on 12v 2amp load and then use like a couple pieces of wire to touch pins 2 & 3 with the positive and ground leads and then reverse the polarity to run the actuator into 4WD and then back into 2WD mode. If your actuator will move in and out by jumpering it, then most likely it is okay and not at fault.

You can test the front diff ADD actuator with vacuum from a vacuum pump and verify that you can turn the driveshaft in 2wd mode and then test the other side and you shouldn't be able to turn the front driveshaft.

I just hate to see people spend that kind of money to only find out it was something else causing the problem.

 

Here's an update:

My wifes 2000 4Runner LTD was stuck in 4WD. Took it to the stealership and they replaced the forward and aft sensors on the top of the t-case ($466.15). That did not solve the problem.

The stealer wanted to replace the actuator on the t-case for ~ $1800.00. Told them I wanted 2nd opinion and took it home. Used the method above to get it back into 2WD + wire on #2 and - wire on #3 and it came out of 4WD just fine. In fact when I reversed the process, it went back into 4WD just fine.

Put it back into 2WD and plugged everything back in. Test drive proved it was back in 2WD. Then manually shifted into 4WD and it went back in just fine but when I shifted it out, back to the blinking 4WD trouble light and stuck again.

Crawled back under the truck, used the power wires to shift it back to 2WD just fine.

Anyone have any suggestions as to what it might be as to why it will shift into 4WD but not back to 2WD? (keep in mind if I crawl under there, and manually operate actuator, it comes out ok)

 

Double,

The good news is that your rear t-case actuator is fine since you can manually get it into 4wd and 2wd mode.

Have you checked the sensor on the front axle up by the front diff actuator yet? This is the one that is causing mine to stick into the blinking 4wd light mode sometimes. I removed mine and tested it with the multimeter by putting the pos lead on 1 pin and the neg lead on the other pin and then pushing the button in. This should give you a continuity beep or a readout on the screen of the multimeter. If it doesn't do anything when it is pushed in, then that sensor is bad.

 

I have pics of the 4wd system if anyone wants some, I can email them to you.

I would post them here, but the size restriction is so small for pics that you wouldn't be able to distinguish what was what on the pictures.

 

Looks like the sensor on the front diff is my next thing to look at - thanks for the heads up. The good news is that the truck is in 2WD and being a street queen in AZ, 4WD doesn't get used that often. I told the wife to just leave the 4WD alone until I can look at it over the weekend.

Anyone have any knowledge as to where the vacuum line going into the trasfer case runs to and how I can test that? I haven't ruled out a dry rotted vacuum hose yet but want to add that to my list of diags this weekend.

 

99SC4Runner...use my host to host the pictures. http://www.picsftw.com

 

I put 6 different documents on there for all to enjoy and learn from.


Doug

 

I installed the new front diff sensor and now my AWD and my 4WD both work awesome. I hope this helps others that are experiencing the same issues I was having. It sure feels good to have my 4WD working like it supposed to

 

Awesome news about fixing your 4WD/AWD!! For $36, I am just going to order it and replace mine. Compared to the $466 (disputing those charges) already spent on the truck, I don't mind.

Do you have a direct link to your scanned images?