[ShooterMcGavin]

My 4wd has been out for a while on my '97 5-speed with the J shifter. I was offroad and switched into 4wd. It engaged 4wd and as I was driving, it began switching in and out of 4wd. After a while, it would switch in and out more quickly - sometimes I would just hear the clicking but it wouldn't actually engage 4wd. Eventually, it stopped going into 4wd at all and I was stuck with 2wd, which is where I sit now. Through all of this, it didn't matter if I was 4H or 4L, 4wd wouldn't engage but low range would still engage (2L).

I have read a lot about the 4wd issue in posts, but I have no idea what the posts are talking about. VSV? Where's that? Where are the vacuum lines that I need to switch to test it? Anyone have a photo? I think testing the vacuum lines is the first step, but even that is holding me back. I'm guessing the vacuum lines are on the front diff? I'll need to remove the skid plates to access those, again I'm guessing.

After I look at the vacuum lines, I think I'd be ready for some deeper investigation. Or, are there some other simple tests I can perform to diagnose at this point? Could the problem be low front diff fluid? I lost some fluid when rebooting a CV.

[TejasRunner01]

Sorry to hear you are having problems. First of all the J shifter means that the transfer case is mechanically actuated, but the front differential still has an ADD vacuum actuator system. So your initial assumption to test the vacuum is wise.

You can see if it is a transfer case problem or ADD problem pretty easily by:

1. Make sure j shifter is in 2wd.
2. Spin the front propeller shaft by hand and see if it will spin freely.
3. With the engine off, try the J-shift in boy hi and low 4wd and see if that front propeller shafts moves. If it stays locked, it isn't a problem with your transfer case.

Here are instructions for troubleshooting the ADD system:

Quote:

VSV’s/ADD
Don't guess at it, troubleshoot! Start at the twin VSV's (Vacuum Switching Valves) on the driver fender wall. There are two long vacuum hoses that come up from the diff, one goes to each VSV. Check to see that one of the two hose nipples on the VSV’s has vacuum (engine running, 4WD NOT engaged. If no vacuum either side, check the check valve going to the intake manifold and look for loose hoses or a hole in the reservoir. If there is vacuum going to one hose, then put it in 4WD. See if the vacuum switches to the other hose. If it does, and no 4WD, problem is the diff actuator or the line to the diff. If it does not, then just switch the hoses and you should go into 4WD. This confirms diff is okay. (Mark the hoses first so you know which belongs where!)

OK, switch them back. Then use a test light to see if electrical signal from the TC also switches sides of the VSV. If it does not, problem is the TC, the switch on the TC, or the TC actuator, or its wiring back to the button (last two for non-J shift only). If it does, but the vacuum does not, the problem is the VSV itself.

I start troubleshooting at the VSV's because you can figure out where the trouble is without having to climb under the truck. [Does not apply to '01-'02].

Good luck mate.


Sent from my A0001 using Tapatalk

[TejasRunner01]

VSV is the vacuum switching valve, it basically is what facilitates which hoses get vacuum and which don't as needed. It is on the drives side near the brake booster. I attached some pictures.

If I was you I would check the fluid but I doubt that is the cause.



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[ShooterMcGavin]

Great! Thanks for all that information. Do you know which hoses from your first photo needs to be switched for testing?

Are the VSVs actually the round things, so 2 VSVs in that 1 box?

[meRockboost]

That pic looks like an emmisons system vsv. Follow the vacuum lines that go to the diff and trace them out. Mine were mounted onto the fender itself driver side. Only 2 lines go to the diff. Switch them.

I had the same problem and it was the 4wd selector switch on the t-case.

[meRockboost]

4wd troubleshooting

[ShooterMcGavin]

Thanks!

I guess I have a couple more questions on the diagnosis...
I should put the J shifter into 2wd and switch the vacuum lines. At that point, it should automatically engage 4wd. Is that correct? (obviously, with the engine running and assuming everything is working properly) Will the 4wd light illuminate on the dash, or do I need to drive it to determine if it has engaged 4wd?

If I am in 2wd and I try to turn the front drive shaft, should it turn freely?

I will have to take my time and read through that link for 4wd troubleshooting.

[thecole1098]

Originally Posted by ShooterMcGavin

Thanks!

I guess I have a couple more questions on the diagnosis...
I should put the J shifter into 2wd and switch the vacuum lines. At that point, it should automatically engage 4wd. Is that correct? (obviously, with the engine running and assuming everything is working properly) Will the 4wd light illuminate on the dash, or do I need to drive it to determine if it has engaged 4wd?

If I am in 2wd and I try to turn the front drive shaft, should it turn freely?

I will have to take my time and read through that link for 4wd troubleshooting.

If you swap the vacuum hoses for the ADD, the front axle will be engaged (which can be tested by seeing if you can spin the front driveshaft) however if the shifter is in 2WD, the dash light will not be illuminated no matter if the front axle is connected or not. To rule out the vacuum issue for the ADD system, swap the hoses with the engine running and check to see if you can spin the driveshaft. If you can’t, good! This means your front axle is connecting correctly. Once you do this and if it still doesn’t work, we can begin diagnosing the transfer case.

Also it’s worty mentioning if your relay even works. Do you still hear a clicking around your passenger sides kick panel when moving the J shifter or just nothing?

[ShooterMcGavin]

Originally Posted by thecole1098

If you swap the vacuum hoses for the ADD, the front axle will be engaged (which can be tested by seeing if you can spin the front driveshaft) however if the shifter is in 2WD, the dash light will not be illuminated no matter if the front axle is connected or not. To rule out the vacuum issue for the ADD system, swap the hoses with the engine running and check to see if you can spin the driveshaft. If you can’t, good! This means your front axle is connecting correctly. Once you do this and if it still doesn’t work, we can begin diagnosing the transfer case.

Also it’s worty mentioning if your relay even works. Do you still hear a clicking around your passenger sides kick panel when moving the J shifter or just nothing?

Thanks for that. YES, I do/did hear a clicking from the ECU when I put the J shifter into 4H. In fact, when the 4wd was going out, it first was clicking constantly as it was trying to engage and disengage the 4wd. Maybe I will need to revisit that and see if it still clicks or not. If it isn't clicking, what does that tell us?

[amalik]

@TheDurk is also a damn BOSS at this issue.

[thecole1098]

Originally Posted by ShooterMcGavin

Thanks for that. YES, I do/did hear a clicking from the ECU when I put the J shifter into 4H. In fact, when the 4wd was going out, it first was clicking constantly as it was trying to engage and disengage the 4wd. Maybe I will need to revisit that and see if it still clicks or not. If it isn't clicking, what does that tell us?

If you hear no clicking, that means the relay is not functioning correctly to complete the circuit to engage the switching valves for the ADD. I honestly don't think the issue lies at the transfer case as these are pretty simple and bullet proof compared to the Limited models and later 3rd gen versions that had the actuators/AWD systems in them. I'm pretty sure your issue will either be the relay needing to be replaced (if there is no clicking when moving the lever) or perhaps even a disconnected vacuum line going from the switching valves on the drivers fender in the engine compartment to the front axle. If it's none of those simple things, it's also possible the switching valves themselves could be bad which can be tested easily by either resistance or perhaps the actuator for the ADD system of the axle went out and is not allowing the axle to connect to the transfer case, which can be tested by swapping the vacuum lines as previously mentioned.

[TheDurk]

Hi. I've been traveling to Brazil to visit my HiLux SW4 so I've been off-net. This is the same setup I have (J-shift, 5-speed) so that helps. @TejasRunner01 was kind enough to post my troubleshooting routine I wrote years ago, but then posted the wrong picture to go with it, which is less than ideal. That is in fact an evap VSV, which is a whole different animal.

Based on your systems, I'd say you should start by checking vacuum integrity. Locate the checkvalve between the manifold and the 4wd VSVs on the fenderwall.

Here is a pic of mine:

https://www.yotatech.com/forums/f2/9.../#post51932302

The checkvalve is that cylinder thingy in the middle of the hose. Make sure there is vacuum on the end of that away from the manifold with the engine running.

Then label the ADD tubes so you can get them back the same way. see pic.

Again, with engine running, pull each in turn. See if one, none, or both have vacuum. Switch J-shift from 2H to 4H. Repeat. Post results and we can go from there. Be precise in your answer and it will save time.

[phattyduck]

Originally Posted by thecole1098

If you hear no clicking, that means the relay is not functioning correctly to complete the circuit to engage the switching valves for the ADD. I honestly don't think the issue lies at the transfer case as these are pretty simple and bullet proof compared to the Limited models and later 3rd gen versions that had the actuators/AWD systems in them. I'm pretty sure your issue will either be the relay needing to be replaced (if there is no clicking when moving the lever) or perhaps even a disconnected vacuum line going from the switching valves on the drivers fender in the engine compartment to the front axle. If it's none of those simple things, it's also possible the switching valves themselves could be bad which can be tested easily by either resistance or perhaps the actuator for the ADD system of the axle went out and is not allowing the axle to connect to the transfer case, which can be tested by swapping the vacuum lines as previously mentioned.

Toyota relays and VSVs are very reliable. Most likely in all this is the position switch on the transfer case. If the relay was clicking on and off, that means the switch was intermittent. If it doesn't click now, the first thing to test is the switches on the transfer case.

-Charlie

[ShooterMcGavin]

Originally Posted by TejasRunner01

Sorry to hear you are having problems. First of all the J shifter means that the transfer case is mechanically actuated, but the front differential still has an ADD vacuum actuator system. So your initial assumption to test the vacuum is wise.

You can see if it is a transfer case problem or ADD problem pretty easily by:

1. Make sure j shifter is in 2wd.
2. Spin the front propeller shaft by hand and see if it will spin freely.
3. With the engine off, try the J-shift in boy hi and low 4wd and see if that front propeller shafts moves. If it stays locked, it isn't a problem with your transfer case.

Here are instructions for troubleshooting the ADD system:

Quote:

VSV’s/ADD
Don't guess at it, troubleshoot! Start at the twin VSV's (Vacuum Switching Valves) on the driver fender wall. There are two long vacuum hoses that come up from the diff, one goes to each VSV. Check to see that one of the two hose nipples on the VSV’s has vacuum (engine running, 4WD NOT engaged. If no vacuum either side, check the check valve going to the intake manifold and look for loose hoses or a hole in the reservoir. If there is vacuum going to one hose, then put it in 4WD. See if the vacuum switches to the other hose. If it does, and no 4WD, problem is the diff actuator or the line to the diff. If it does not, then just switch the hoses and you should go into 4WD. This confirms diff is okay. (Mark the hoses first so you know which belongs where!)

OK, switch them back. Then use a test light to see if electrical signal from the TC also switches sides of the VSV. If it does not, problem is the TC, the switch on the TC, or the TC actuator, or its wiring back to the button (last two for non-J shift only). If it does, but the vacuum does not, the problem is the VSV itself.

I start troubleshooting at the VSV's because you can figure out where the trouble is without having to climb under the truck. [Does not apply to '01-'02].

Good luck mate.


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I made some progress today. I switched the hoses going into the VSV closest to the firewall. Results... I saw my 4WD light come on for the first time in years!!! And I tested - it was really in 4WD. I was excited. With the hoses switched, I could switch into 4WD and it would go into 4WD. I could switch out of 4WD and it would go out of 4WD. Then I switched the hoses back to normal and the use of 4WD started working properly for a while. I could go in and out of 4WD. However, in all cases, it was sometimes difficult to get it back into 2WD.

TejasRunner01, that was a great writeup you provided. Thank you. Now, I need to start going through all the steps you have listed.

Does anyone have any conclusions for me like "great, all you need to do is change out vacuum hose X"? Crossing my fingers

[TheDurk]

Originally Posted by ShooterMcGavin

I made some progress today. I switched the hoses going into the VSV closest to the firewall. Results... I saw my 4WD light come on for the first time in years!!! And I tested - it was really in 4WD. I was excited. With the hoses switched, I could switch into 4WD and it would go into 4WD. I could switch out of 4WD and it would go out of 4WD. Then I switched the hoses back to normal and the use of 4WD started working properly for a while. I could go in and out of 4WD. However, in all cases, it was sometimes difficult to get it back into 2WD.

TejasRunner01, that was a great writeup you provided. Thank you. Now, I need to start going through all the steps you have listed.

Does anyone have any conclusions for me like "great, all you need to do is change out vacuum hose X"? Crossing my fingers

Sorry, but your journey has just begun. The good news is your front diff is working fine and that is the hardest to fix. Next, you need to take a meter or test light to that VSV and test each side for voltage in 2wd and 4wd. If it switches sides, you have a bad VSV. If not, problem is upstream, typically a switch on the TC.