Don't hate me - flashing 4wd light

[RPS99SHO]

Cross-posted from the massive YT thread about this issue, but hoping to get more views and maybe a resolution quick since I'm home from work today.

I bought my 99 Limited auto with 194k back in January. Up until a few days ago, the 4wd system worked without issue. Few days ago, when trying to engage AWD, I got the blinky 4wd death lights. Here is what I have done. Removed and tested continuity in the front diff switch/sensor, the two switches that I could get to on top of the TC. All 3 tested fine. I checked out the VSV, determined the unit was getting vacuum past the check valve, and checked the fuse. With the button off, and the lights blinking, the front driveshaft was locked, as I suspected. I think the system got itself into 4 at some point when the light was flashing. I did the vacuum switch trick to get the system back into 2, and tested the front driveshaft. It rotated freely. Reversed the lines and the front driveshaft locked again. So the actuator on the front axle is good. For right now I have the lines oriented in such a way that it's in 2, which is what I want for now. I think the lines are backward from where they should be. So this tells me that either the VSV is bad, or is getting bad/no information from the TC. This is where I'm stuck. I could use direction on the next steps, please. Thanks!

 

[Kyle Reese]

dude all that means is that it's engaging hahaha

 

[kurticus91]

Yeah im not sure about the death lights, but Kyle Reese is right that it flashes while engaging. I'm usually coasting at low speed when I engage 4WD. Have it in drive, click on the 4WD, and let off the gas and let the truck coast. It should flash for a moment and then go solid green. Good luck!

 

[jgue467]

...Up until a few days ago, the 4wd system worked without issue. Few days ago, when trying to engage AWD, I got the blinky 4wd death lights....

That's a lot of doing. Have you done what the owner's manual and the card under the driver visor say to do when you get the "blinkys"?

If that doesn't work then PM "The Durk" - he'll set ya' straight!

:cowboy:

 

[RPS99SHO]

I'm well aware that the lights blink while engaging or disengaging. The 4wd lights flash 100% of the time right now, no matter the drive mode.

I'm sure Durk, the 4Runner Lord and Savior will chime in either here or at YT sooner or later. My search turned up the fact that he responds to each and every one of these threads.

 

[BirdieKing]

Mine was doing this just a couple days ago -- I don't offroad, so I literally never click the button, but I bumped it, then the lights wouldn't go off. Eventually (3 days), they randomly stopped, I didn't do anything to my knowledge to make this happen, it just did. BUT during those 3 days I did a bunch of research.

It looks like all your stuff checks out from a connectivity stand point, no? If it does, I think you may need to replace a couple sensors. See the below links for more info.

4WD won't disengage on 99 4Runner LTD - YotaTech Forums

http://www.toyota-4runner.org/3rd-gen-t4rs/80433-flashing-4wd-indicator-light.html

 

[TheDurk]

Well, sounds like you are on the right track. Next is to determine if it is indeed the VSV or the signal from the 4wd ECU. That takes using a test light to see if the 12V+ signal switches back and forth from one VSV to the other as you go from 2wd to 4wd. If it does, bad VSV for sure. If not, time to start checking whether the sensor inputs are actually reaching the 4wd ECU, since you are saying the switches test good. Hoping it's the VSV, because the alternatives are a little hairy if it's not the sensors. Post back, and I'll help with next steps.

It is also important to check both 4H and 4L, as different sensor switches are involved. Sometimes 4L works and 4H does not and we need to know.

Here is a present from my '99 paper EWD manual.

 

[RPS99SHO]

Forgive my electrical ignorance. Where on the VSV would I probe the light to confirm receipt of signal from the 4wd ecu?

I have not tested any of the 3 sensors on top of the TC, as I haven't ripped apart the interior to get to them, so my issue could still be lurking there. My concern is if I do try out 4HL and 4L, I may not be able to get back to 2wd. Any danger of that happening?

I'm also wondering if maybe my issue lies with water/ debris intrusion into the TC actuator. Can I remove the 3 screws and remove the metal cap without worrying about retiming?

Thanks for your input.

 

[TheDurk]

Forgive my electrical ignorance. Where on the VSV would I probe the light to confirm receipt of signal from the 4wd ecu?

There is a plug for each VSV. Both have a white-black wire that is a ground. One has a green-red wire, and that should be hot in 2wd. The other has a solid light-green wire, and that should be hot in 4wd. You can take the plugs off the VSV for this test to make it easier to probe the plug contact. Also, make sure only ONE of the two wires is hot at any one time.

I have not tested any of the 3 sensors on top of the TC, as I haven't ripped apart the interior to get to them, so my issue could still be lurking there. [Ah, I thought you had tested them all. That's good news.]My concern is if I do try out 4HL and 4L, I may not be able to get back to 2wd. Any danger of that happening?

I wouldn't think so. As it seems to go into 2wd ok if vacuum is in the correct hose, that makes me think it will go back.
I'm also wondering if maybe my issue lies with water/ debris intrusion into the TC actuator. Can I remove the 3 screws and remove the metal cap without worrying about retiming?

Nothing you have said suggests the TC actuator is not working correctly. FFS, don't try fixing something that ain't broke. Those electric actuators are tricky. Trace the fault first before taking stuff apart.

Thanks for your input.

My answers in bold.

 

[RPS99SHO]

You da man, Durk. I'll rip into it again today. If the VSV tests fine then the remaining tests for the PITA sensors will need to wait until next week, since I need the truck to be operational Sat for the diff fluid changes, and I don't have a sensor socket.

 

[RPS99SHO]

Did some probing and discovered that the blue connector at the VSV (puts front diff in 4wd) has power all the time. No matter the status of the AWD button or the position of the 4wd shifter. The brown connector never gets power.

On my very short test drive I couldn't get it into 4HL.

 

[TheDurk]

Did some probing and discovered that the blue connector at the VSV (puts front diff in 4wd) has power all the time. No matter the status of the AWD button or the position of the 4wd shifter. The brown connector never gets power.

On my very short test drive I couldn't get it into 4HL.

Yep, test the other sensors.

 

[RPS99SHO]

I know the sensor on the passenger side is the center diff lock sensor. The other two on top - what are they? I assume one of them is responsible for telling the VSV to switch from 2 to 4?

 

[TheDurk]

I know the sensor on the passenger side is the center diff lock sensor. The other two on top - what are they? I assume one of them is responsible for telling the VSV to switch from 2 to 4?

I don't know for sure because I have a different T/C on mine (the J-shift). But on mine, the two on top are the senders for 4H on one side and 4L on the other.

On yours, I'm guessing the prime suspect is whichever one has the brown wire with yellow stripe. You can match the function with the wire color looking at the wire diagram I posted upthread.

 

[RPS99SHO]

Anyone have a write-up handy about how to access the TC sensors through the center console?

 

[suppra87]

Does this help as to determining which sensor is which? Pulled it from a yotatech thread you may or may not have seen.


Also, although I'm not 100% on this, you may be able to access the switches from the bottom. Use a jack to support the trans crossmember while you unbolt it from the frame and lower the trans down 2" or so to gain access. There should be enough room.

 

[RPS99SHO]

Does this help as to determining which sensor is which? Pulled it from a yotatech thread you may or may not have seen.


Also, although I'm not 100% on this, you may be able to access the switches from the bottom. Use a jack to support the trans crossmember while you unbolt it from the frame and lower the trans down 2" or so to gain access. There should be enough room.

Funny you should chime in. I just asked you in my build thread about blocking off shop time for me next weekend. If you think that's the best way to attack it, we can certainly try that.

And the switches that need to be pulled and checked are the neutral position, L4, and center diff switches. I suspect the center diff switch is the one causing my issues.

 

[RPS99SHO]

Changed the rear diff and TC fluid today. Backing out of the garage, I heard a solid think from the front end. 4wd engaged. Flashing light went away. Tested 4H functionality - all good. When I get a chance to get off pavement I'll test 4HL and 4L. Maybe the fluid change was the ticket? Also could be the 65° temps today. We'll see when it gets colder.

 

[cutlass]

Changed the rear diff and TC fluid today. Backing out of the garage, I heard a solid think from the front end. 4wd engaged. Flashing light went away. Tested 4H functionality - all good. When I get a chance to get off pavement I'll test 4HL and 4L. Maybe the fluid change was the ticket? Also could be the 65° temps today. We'll see when it gets colder.

So, did you determine that this did the trick for you?

 

[RPS99SHO]

So, did you determine that this did the trick for you?

Every time I have tried it since, it has worked. I have limited my time in 4wd until I can change out the front diff fluid this weekend. Seeing the condition of the TC and rear diff oils made me not want to use 4wd until it's nice and fresh.