4WD VSV Harness?

Hi all, first post here...but the forum has already been very helpful! I have a vacuum actuated ADD that seems to not be working - can shift into 4H and 4L via the J shifter but no light on the dash. Here's what I've done so far:

1. Confirmed that the harness into the ADD relay gets 12V when I shift from 2H to 4H
2. Did all the relay troubleshooting steps in the Haynes manual - the relay seems ok
3. The red/brown VSV harness switches between 0V/14V when shifting in and out of 4H
4. The blue VSV harness remains at 0V when shifting in and out of 4H

Am I correct in thinking that if the relay gets 12V and seems to be functioning ok itself, then problem is likely in the harness to the blue VSV (and that the transfer case switch is functioning correctly)?

Not sure how hard it is to replace that harness, so wanted to check my thinking first. Thanks!

 

Are you getting vacuum to the actuator on the front diff with the engine running in 4H?

 

Haven't checked yet as I thought I'd found the issue, but I suppose that would tell me for sure.

 

If your missing vacuum but you have power to the solenoid valve you either have a bad valve or broken vacuum line.

 

Thanks, I'll check the vacuum at the actuator. Thought it might be in the harness to the solenoid though, as the one solenoid remains at 0V when switching in/out of 4H, and the other switches 0V/14V.

 

Don’t let me mislead you too much, as a 2nd gen owner. Though I think the vacuum is completely innocuous and will never be a cause. Most likely even in first gens seems to be that front ADD actuator.

However, you mention no blinking whatsoever so save yourself some drained oil and headaches.

Have you checked continuity at your switch, and then your sensor? No reaction at the sensor pushes me toward poor electrical rather than the more common flashing issue. Good luck bud

 

The earlier 1st gens used a vacuum operated ADD actuator controlled by a vacuum solenoid instead of an electronic ADD actuator like our 2nd gens use.

 

I'll double check the solenoids again before moving onto the actuator to confirm no vacuum there. I'd expect the voltage to switch between the two solenoids when shifting in/out of 4H. Thanks all!

 

Interesting, I thought I saw otherwise on Tundras but I like learning from actual owners, so good to learn that. I know they’re not always the same but they run so close.

On that note if you tried to clean & re-grease everything with dielectric I would check into the above. Keeping in the replies for more context later on. Cheers.

 

I'm not a Toyota expert by any means I just try use my knowledge and experience from working on other vehicles and reading service info to understand how the systems work the best I can.
Ford has used a vacuum system for years on their trucks except they use vacuum hubs instead of an axle disconnect, Jeep and Dodge used a vacuum axle disconnect on some of their stuff too but they had a switching valve on the transfer case instead of an electronic one.

I found a wiring diagram, looking at it one solenoid should have power in 4wd the other in 2wd, if you have power at the 4wd solenoid it should be providing vacuum to the front axle. The only way for the indicator to light is for both the transfer case switch and the ADD switch to be closed.

 

Welcome to TacomaWorld
If it goes into 4Hi and 4Lo like you say it may just be the cluster bulb out.
Unless I missed something about front DS spinning by hand in 4wd.

 

The real question did it ever work?? The light does work ??

when was the last time it was used ??

vacuum hoses do dry rot VSV`s do go bad on the vacuum side

the actuators do tend to hang up if not used.

Since I get stuck in my drive way often mine gets used all the time

 

The light did work - last used in 4WD a few months ago. I'm able to shift into 4HI / 4LO via the J-shifter but the front driveshaft is never connected (edit: front driveshaft connected, but front axles aren't locked). Thanks for the wiring diagram Dm93, I'll confirm that I'm not getting power to the 4WD solenoid. Looks like that harness comes right from the relay so if the relay gets power and is functioning the issue would be in that harness. Can also verify that no vacuum is coming from the 4WD solenoid or verify at the ADD actuator that it's not getting vacuum. Thanks for the help so far everyone!

 

If your saying shifting into either 4 High or Low does not spin the front driveshaft that is a mechanical issue .

Do you mean the front axles are not being locked ??



Someone get the transfer case shifter installed wrong ??

That most times results in the case being in neutral

 

Yep sorry, I mean the front axles are not being locked. Did some more troubleshooting this morning and interestingly, things are back to working as normal. I did the following:

- Verified that the vacuum wasn't switching from one solenoid to the other
- Verified continuity between the ADD relay plug and the solenoid plugs (so that harness seems fine)

After moving around the harness that plugs into the relay, I noticed that it was stuck with a constant 12V regardless of whether in 4H or 4L. I plugged in the harness and turned on the truck, and there was the 4WD indicator light. With a little more movement on that relay/harness, everything now seems back to normal - I hear the relay switching each time I shift in/out of 4H and the indicator light goes on/off. I've switched into and out of 4H ten or so times successfully. Makes me think that there is an intermittent short somewhere in the cable running to the relay?

 

I think you mean intermittent open circuit .

A short means open circuit protection melted wires or a visit from the Fire department .

Might be just corrosion or poor connection on the plug now cleaned up by just unplugging and plugging

 

Good point. I guess I’ll see if it remains in working condition. Thanks for the help here all. Interesting to learn how these work...