4W Drive stuck on?

[Bob62]

Switched on the 4WD with no problem. Green light came on and system engaged nicely. A few days later I went to turn it off; unlocked the hubs; and released the green 4WD dash button. Button stays lit when button is out..

Is solenoid bad? Is the 4WD stuck on? Hubs are free, so is it posing any risk to keep driving with it?

 

[gimme a 60]

You can physically suck on the top vacuum pot, all you need to do is take off the hose.

If that fixes it you may have a vacuum leak.

 

[OSS]

Crawl under the truck and try to turn the front driveshaft by hand. If it turns freely, then 4WD is not engaged.

 

[Godwin]

Switched on the 4WD with no problem. Green light came on and system engaged nicely. A few days later I went to turn it off; unlocked the hubs; and released the green 4WD dash button. Button stays lit when button is out..

Is solenoid bad? Is the 4WD stuck on? Hubs are free, so is it posing any risk to keep driving with it?

Vacuum switch on the firewall is bad. Swap the position of the vacuum lines on the switch and you can disengage the front drive.

 

[Bob62]

Vacuum switch on the firewall is bad. Swap the position of the vacuum lines on the switch and you can disengage the front drive.

Thank you. The vacuum switch is the solenoid.?? I changed it years ago and will do so again. Anybody have a new one?

 

[Godwin]

This is the part number 8544060120 but I think it's been discontinued by Toyota. Alternative solenoids have been posted in the past.

 

[diesellibrarian]

Thank you. The vacuum switch is the solenoid.?? I changed it years ago and will do so again. Anybody have a new one?

It could also be a leak in the vacuum line between the solenoid and the transfer case. That's a much cheaper/easier fix, so might be work investigating before you head to the wrecker to find a replacement VSV.

 

[Bob62]

Thanks for helpful comments.

I installed two new Denso vacuum solenoids. 4W light still stays on and 4WD remains engaged. Is it possible that the push button switch itself is bad? It doesn't go off when released. There's vacuum : when you take the hose off you can hear the whoosh. And when you plug in the two colored electric plugs, you hear it go on.

 

[diesellibrarian]

You've checked that the front drive shaft won't spin by hand even after disengaging the 4WD and unlocking the hubs?

Anyway, when in doubt, consult the Factory Service Manual. Here are some screencaps that might be helpful:

It's possible for the switch to go bad - that happened to me. I replaced the stock switch with an ON/OFF/ON toggle switch from an auto parts store. It worked fine: flip the switch one way, and it puts the system into 4WD; flip it to the other "on" and it pulls it out of 4WD.

The other possibility is that the diaphragm on the transfer case has gone bad and is no longer responding to vacuum input.

 

[Godwin]

You've checked that the front drive shaft won't spin by hand even after disengaging the 4WD and unlocking the hubs?

Anyway, when in doubt, consult the Factory Service Manual. Here are some screencaps that might be helpful:

View attachment 3243833

View attachment 3243834

View attachment 3243835

View attachment 3243836

It's possible for the switch to go bad - that happened to me. I replaced the stock switch with an ON/OFF/ON toggle switch from an auto parts store. It worked fine: flip the switch one way, and it puts the system into 4WD; flip it to the other "on" and it pulls it out of 4WD.

The other possibility is that the diaphragm on the transfer case has gone bad and is no longer responding to vacuum input.

Is the diaphragm under constant vacuum in either one direction or the other?

 

[diesellibrarian]

Is the diaphragm under constant vacuum in either one direction or the other?

That's my understanding, yes.

 

[Godwin]

That's my understanding, yes.

Just checked a parts diagram and there is a vacuum port on the dorsal and ventral sides of the diaphragm..

 

[Godwin]

Thanks for helpful comments.

I installed two new Denso vacuum solenoids. 4W light still stays on and 4WD remains engaged. Is it possible that the push button switch itself is bad? It doesn't go off when released. There's vacuum : when you take the hose off you can hear the whoosh. And when you plug in the two colored electric plugs, you hear it go on.

The other possibility is that the diaphragm on the transfer case has gone bad and is no longer responding to vacuum input.

Attach a Mityvac to one of the vacuum connections and leave the other open then pump the Mityvac to create a vacuum and see if the vacuum holds. If not the diaphragm is likely compromised.

 

[Bob62]

All very helpful, thanks. But if the 4WD switch were good, wouldn't the green light go out when released, regardless of what the 4WDrive itself does?

 

[diesellibrarian]

No, because the light is actually controlled by the 4WD control relay (see wiring diagram above).

That's because when you engage 4WD using the lever that puts the system into 4L, it has the same effect as the switch, i.e. it engages the front drive (albeit in 4L) and turns on the light.

EDIT: Actually I'm not reading the diagram right, haha. But in my mind, that's how it works. I need to go back and have a better look at that diagram.

 

[Bob62]

Thanks to all for helpful comments.

Latest is that the mechanic unbolted the diaphragm and temporarily removed the metal arm inside. Light went off and drive shaft spins. We're out of 4WD at least.