1995 Tacoma 3.4l front diff/4x4 issue.. VSV?

I can't shift into 4x4... been searching down rabbit holes and can't find what I need.

I do not think it is a problem with the actuator or at the transfer case...because I can get it to work by switching the vacuum lines at the actuator. I am beginning to think it is one side of the VSV. However, I do not know how it works and what to look for, so any help would be appreciated.

-VSV: I have vacuum on the brown side. Blue side there is no vacuum. Is that normal?
-The dash light does not come on when I switch the vacuum lines at the actuator, but I can tell front diff is engaged.

I had charging issues prior to it going out. Worked fine before that. I Replaced battery and alternator. I also found negative battery cable issues, so I replaced it also. Figured that might be the problem but still not functioning.

Thanks for any help.

 

Have you checked the 4WD fuse in the cab?

Do you have the J-shift transfer case or the push button 2-4 selector style?

It sounds like an issue with the 4wd switch, 4wd fuse, or 4wd ECU not switching vacuum to the blue vsv to pull the ADD selector fork into the 4wd position.

 

4WD fuse is good.

I have the push button 2-4 selector with 5 speed.

 

Take a look in @Red_03Taco thread here.

https://www.tacomaworld.com/threads/help-with-diagnosis-4wd-not-working.817804/

 

Thanks! I'll see if I can work through that and sort it out.
I appreciate it.

 

Let me know if you have further questions

 

Will do. I have some electrical anomalies and why I think a lot of this is related. Thought the ground cable would solve most of it... but now clutch in by itself won't start truck. I have to push the clutch override button on the dash. SMH

 

@Dm93 and @TnShooter can most likely walk you through any electrical issues

 

It's been super busy for me.
Here is a diagram until we can get around to replying.
I'm guessing a bad connection. Study the diagrams and try to get a good understanding of the system.
In short, you 4WD ecu needs to see the correct signals. Which are typically ground inputs.

 

I checked the VSVs. I attempted to check continuity by trying to follow this from @Strictlytoyz on another thread he shared. I don't have continuity on either the orange (or brown?) side or blue side with button push. But I'm not sure if I did it right. Seems pretty straight forward but maybe I am doing it wrong. Orange side has vacuum. Blue side does not. I tried switching the lines top side, nothing changed...though I was able to get it to work by doing that underneath yesterday.

I checked ground for underhood w/b wire it is solid and confirmed.

I checked voltage. Orange side getting 14.2 ish Blue side 19-20mV. I'm sure that's not right.. I checked with button on and off and same reading both times.

Also, sometimes (not every time...but 50% of the time it works every time) if 2-4 button is depressed before ignition on, I get the flashing 4x4.

So I am thinking this is a VSV problem on the Blue side...since I assume that switch allows vacuum to 'switch' to the diff actuator and it's not doing that.

 

So the 4wd light doesn't come on or flash every time? Have you verified continuity at the 2-4 push button?

 

Correct...but with the vacuum issue, I sorta ruled that out. I'll check it though if you think I should. Even when it decides to flash, there's no power or vacuum at the VSV.

 

Can you verify you have good continuity between the add control relay to the vsv solenoids?

 

I’ll look for the relay, but in another thread someone mentioned the push button style doesn’t have one. If that’s inaccurate, let me know but I think I know what I’m looking for. Testing it might need help.

 

The 4WD ECU controls the VSV operation on the push button, not the relay.

 

Thanks guys.. When I find the ECU, I am assuming I could test the V2 and V4 somehow to ensure I am getting power to the VSV having issue. Seems to me, that would be an unlikely cause but a good way to rule out ECU.

If it is the VSV, which I am thinking it is, where do I get one and is there a brand that works best? Junk yard?

Thanks for all the help.

 

Actually, I may take that back. With all my electrical gremlins, it could be the ECU. I'll keep digging.

 

Here is a very short and brief description of how the 4WD system works.
You press the 4WD button, this sends a signal to the 4WD ECU.
The 4WD ECU then turns on the 4WD 2-4 motor on the transfer case.
Once the transfer case is in “4WD”, it then sends a signal to the 4WD ECU to turn on the VSV for the front differential.

Most of the time, you are missing a “signal” to the 4WD ECU.
The signals are “ground” inputs. If you look close at the diagram I posted in post #9, you will see that all the inputs are sent through the switches. Once the switch is “closed” it sends a ground “signal” to the 4WD ECU.

 

I see that now. It looks like the push button sends a ground signal to the ecu when closed. If not, then no power would be sent to the VSV.
I'll see if I can test the push button with the info @Strictlytoyz sent earlier.

Am I understanding that correctly? Thanks

 

That's right.
FWIW, it's not usually the switch inside the truck.
It's typically one on the transfer case or ADD.

If I were betting, I'd bet one of the below.
Notice that the 2-4 Select Motor has a switch too.