4WD Light is ON but but diff doesn't work so no 4WD! HELP HELP HELP

achha64

achha64

New member
Hi all, I really need your help! My 4WD stop working at the middle of the trail.

Here is the symptom: When I push my 4H button the 4x4 Dash light come on as well as when I push it to 4L, the Dash light still there! but the front wheels doesn't spin.

So I troubleshoot a few different points!
Please have a look on the 3 images (they have text to explain)

I don't want to bring this to the dealer or shop!
Want to know first what is the cause!

921411_10153909099457859_7706303412581224936_o.jpg


10623445_10153909099467859_6850532208374637342_o.jpg


12377718_10153909099472859_8081303562580554282_o.jpg
 
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achha64 said:
1997, Limited! The 4WD Lights doesn't flash! It's just turn on as normal! I push the 4WD button and the 4WD come on as a normal working condition 4WD
Click to expand...

Sounds like your front differential is completely out then. Could be electrical...
I can't remember what years have a vac. controlled diff.
 
Bijan said:
Sounds like your front differential is completely out then. Could be electrical...
I can't remember what years have a vac. controlled diff.
Click to expand...

If you see in the pics that I posted I have 2 Vacuums line that goes to the front diff. my truck is a A.D.D and all is controlled by the vacuums line!

Have a look at the Vacuums lines explanation image that I have! let me know if this make sense or not
 
achha64 said:
If you see in the pics that I posted I have 2 Vacuums line that goes to the front diff. my truck is a A.D.D and all is controlled by the vacuums line!

Have a look at the Vacuums lines explanation image that I have! let me know if this make sense or not
Click to expand...

I am not sure if this is the issue but you might check the front differential sensor. (Toyota Part#84222-35070) This little sensor is pretty critical to our 3rd Gen 4WD's and many stealerships have been caught trying to sell you a $2K+ repair job when this $43 part/sensor is the culprit. It is a tight fit to get to it (on the front differential) and requires a 27mm socket to remove. Some folks have had luck removing it, cleaning it well and reinstalling. Might be worth a shot. Good luck!
 
Something does not make sense here. If you are really not getting vacuum passed by either of the VSV's (Vacuum Switching Valves) then nothing is going to move your front diff actuator and then nothing is going to turn your light on. If light is coming on, and no drive on front wheels, then front actuator is not engaging the axle sleeve and there HAS to be vacuum to the front on one hose because the light means the actuator has tried to engage and the sensor says it did. Possibly you have a bad sensor showing engaged all the time AND you have a defect in the vacuum system.

Check to see if the 12V signal switches from one side of the VSV to the other. If it does, you need a new VSV AND a new front diff sensor. If not, time to check T-Case sensors.

Are you sure you checked the nipple on the VSV for vacuum, or did you maybe check the hoses that go to them?

As it is a pushbutton, there is no ADD relay; there is a 4wd computer in the left kick panel. The ripped vac line is not part of the ADD system, but a bad enough vac leak anywhere can mess up the ADD system. I don't think that one is bad enough.
 
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TheDurk said:
Something does not make sense here. If you are really not getting vacuum passed by either of the VSV's (Vacuum Switching Valves) then nothing is going to move your front diff actuator and then nothing is going to turn your light on. If light is coming on, and no drive on front wheels, then front actuator is not engaging the axle sleeve and there HAS to be vacuum to the front on one hose because the light means the actuator has tried to engage and the sensor says it did. Possibly you have a bad sensor showing engaged all the time AND you have a defect in the vacuum system.

Check to see if the 12V signal switches from one side of the VSV to the other. If it does, you need a new VSV AND a new front diff sensor. If not, time to check T-Case sensors.

Are you sure you checked the nipple on the VSV for vacuum, or did you maybe check the hoses that go to them?

As it is a pushbutton, there is no ADD relay; there is a 4wd computer in the left kick panel. The ripped vac line is not part of the ADD system, but a bad enough vac leak anywhere can mess up the ADD system. I don't think that one is bad enough.
Click to expand...


Sorry to sound a bit stupid on that but how do i check the the 12V signal switches from one side of the VSV to the other?
 
achha64 said:
Sorry to sound a bit stupid on that but how do i check the the 12V signal switches from one side of the VSV to the other?
Click to expand...

Get a 12V test light and clip the wire to battery negative post. With engine running and in 2wd, pull one plug off the VSV and probe both contacts. Then do the plug on the other VSV. Switch to 4wd and repeat. One of the two contacts on one side should light the lamp. In 4wd, one of the two on the other side should light the lamp.
 
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TheDurk said:
Get a 12V test light and clip the wire to battery negative post. With engine running and in 2wd, pull one plug off the VSV and probe both contacts. Then do the plug on the other VSV. Switch to 4wd and repeat. One of the two contacts on one side should light the lamp. In 4wd, one of the two on the other side should light the lamp.
Click to expand...

I went double checking the Vaccs line from the Nipple! the Nipple that connect to the line that goes to the diff has no Vaccume at all! but the one that come from the manifold and canister has it!
 
achha64 said:
I went double checking the Vaccs line from the Nipple! the Nipple that connect to the line that goes to the diff has no Vaccume at all! but the one that come from the manifold and canister has it!
Click to expand...

There are TWO lines that go to the diff. Each has a nipple, and ONE nipple only should have vacuum when the engine is running. Vacuum should switch to the OTHER nipple when 4wd is called. The VSV's do that by responding to the 12V+ signals they get from the 4wd ECU.

So you need to check in 2wd AND 4wd, and see if it changes between the two.
 
TheDurk said:
There are TWO lines that go to the diff. Each has a nipple, and ONE nipple only should have vacuum when the engine is running. Vacuum should switch to the OTHER nipple when 4wd is called. The VSV's do that by responding to the 12V+ signals they get from the 4wd ECU.

So you need to check in 2wd AND 4wd, and see if it changes between the two.
Click to expand...

I made a video here have a look and let me know

https://www.youtube.com/watch?v=4UKdMiWG9No
 
TheDurk said:
Ok. No vacuum getting past VSV. (Short version of two minute film.)

Now you need to do electric test I posted above to know if problem is in VSV or elsewhere.

Did you check 4wd fuse? Use a light, a meter, or a known good fuse. Do NOT tell me "It looks fine.."
Click to expand...

I will check the fuse but what a bad 4WD will do ?
 
achha64 said:
Did the Light testing! No light on both VSV plugs! in 2WD or 4WD! and 4WD Fuse work well! so what is the culprit now?
Click to expand...

Well, it's NOT the VSV's. They are doing just what they are supposed to. Problem is electrical. We still have work to do to see where the issue is. Next thing is to see if the 4wd ECU is calling the T/C to engage 4wd or if it is totally dead. So I need you to first have it in 2wd and verify that the front driveshaft spins freely with your hand. Start the engine and put it in 4wd. Check the front driveshaft again. Did it lock up?

Meanwhile here is the circuit diagram so we both know what we are looking at. Do not despair, we will get this.

http://www.toyota-4runner.org/attachments/3rd-gen-t4rs/174093d1443321407-4wd-problem-4wd-2-4-select-switch.pdf
 
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TheDurk said:
Well, it's NOT the VSV's. They are doing just what they are supposed to. Problem is electrical. We still have work to do to see where the issue is. Next thing is to see if the 4wd ECU is calling the T/C to engage 4wd or if it is totally dead. So I need you to first have it in 2wd and verify that the front driveshaft spins freely with your hand. Start the engine and put it in 4wd. Check the front driveshaft again. Did it lock up?

Meanwhile here is the circuit diagram so we both know what we are looking at. Do not despair, we will get this.

http://www.toyota-4runner.org/attachments/3rd-gen-t4rs/174093d1443321407-4wd-problem-4wd-2-4-select-switch.pdf
Click to expand...

The front shaft spin free in 2WD engine or off! and once I put in 4WD the front shaft lock cannot spin anymore! Whats next?
 
achha64 said:
The front shaft spin free in 2WD engine or off! and once I put in 4WD the front shaft lock cannot spin anymore! Whats next?
Click to expand...

Well, I think we are down to a faulty 4wd ECU or a connection issue between the ECU and the VSV's. We can rule out the transfer case switches, power issues, and 2-4 button issues because the T-case is being engaged and disengaged as it should. So I need you to access the 4wd ECU in the left kick panel and use your test light to check for voltage on Terminal 11 (solid light-green wire) and Terminal 4 (purple wire with green stripe) and do this in both 2wd and 4wd.

I also would like you to confirm whether ADD engages in L4 by any chance. I doubt it, but it is something we need to check.
 
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TheDurk said:
Well, I think we are down to a faulty 4wd ECU or a connection issue between the ECU and the VSV's. We can rule out the transfer case switches, power issues, and 2-4 button issues because the T-case is being engaged and disengaged as it should. So I need you to access the 4wd ECU in the left kick panel and use your test light to check for voltage on Terminal 11 (solid light-green wire) and Terminal 4 (purple wire with green stripe) and do this in both 2wd and 4wd.

I also would like you to confirm whether ADD engages in L4 by any chance. I doubt it, but it is something we need to check.
Click to expand...

Which one is the 4WD ECU?
10636605_10153928789007859_441473689472150652_o.jpg
 
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