gfrench

I have a 94 4Runner with automatic transmission and that damn push button 4wd. It has always worked fine up until this ice storm when I actually needed it.

I did some research and checked all of the lines. They all seem to have vacuum, but there is one specific question I have. Up on the passenger side there are 2 pieces with vacuum lines and electrical plugs which I believe are the ADD solenoids. The fwd one has an orange plug, and the aft one has a blue plug.

When I pull the upper vacuum lines, both have suction, but when I pull the lower ones, the orange one has suction and the blue one does not. Is this normal, or is this my problem?

RJR

One should have suction and the other one not, depending on if you are in 4wd or 2wd. Try changing from 2wd to 4wd and see if the suction changes from one to the other. If it does, the vacuum solenoids are not your problem. If it doesn't, it probably means the ADD relay isn't switching (it responds to a signal from the transfer case when you switch into 4wd and activates the ADD system through the vacuum valves.)

Edit: Just checked the wiring diagram, and if I'm reading it right, the blue one should have suction in 4wd. The orange one should have suction in 2wd. If only the orange one ever has suction, your ADD is disconnected, and with an open diff, you will not have 4wd performance.

In a pinch, just swap the two vacuum lines. That will pull the ADD in continuously, and allow to you operate in 4wd till you figure out the underlying issue. The transfer case will still shift into 2wd, so you can drive on dry streets. The only difference is that your entire front drive train will be spinning, so mpg might go down a bit. No different than driving around with manual hubs locked in.

RJR

Actually, a better way to bypass the system is to pull off the two top vacuum lines. Plug one, and connect the other one directly to the lower vacuum line that was plugged into the blue vacuum solenoid. That way the ADD will stay locked in even if your electrical circuit decides to start working again at an inopportune time.

gfrench

Thanks. I switched the lines before I made my original post, but still had nothing- or at least no "4WD" light on my dash. I'll re-try, but pay more attention to what happens and make sure I connect it every way I can. Is there a fuse somewhere that I can check?

gfrench

Ok. Update- I pressed the 4wd button and it did not change suction from orange to blue. Orange stayed sucking.
I switched the lines and pressed the 4wd button. No light came on, but I don't know how to tell if it is in 4wd. I didn't hear anything engaging or anything. Is my blue plug not getting power? Is there a fuse or relay or something I can change to get it working again?

RJR

You can't easily hear the ADD shifting, but if the 4wd light is still off, it's likely not engaged. The best way to figure out if the ADD is locked in is to put the truck in 4wd with the engine running (so the ADD has vacuum), jack up one front wheel, and try to spin it. If you can turn it, the ADD is not locked. If you can't, it is.

You should be able to hear the ADD relay click when you shift the transfer case from 2wd to 4wd. It's under the dash right near the steering column. You can also hear the vacuum solenoids clicking if they're working. If you don't hear anything clicking, you have an electrical problem.

I'll have to check the wiring diagram to let you know about fuses, etc.

gfrench

Those were the sounds I was listening for. There was no clicking or anything.

gfrench

Ok...Electrical update:
The 4WD switch on the shifter works. When I press it in, I hear the relay under the dash click.
The orange plug is getting power with the 4WD switch pushed and not pushed.
The blue plug never gets power.
Switching hoses does nothing. The wheel spins free no matter which hose is connected to the sucking plug.
Now I am even more lost than before.

scope103

I don't have the pushbutton-only 4wd engagement, but:

My diagrams show that the wire to the 4wd VSV is Purple-Green (with ground White-Black). The wire to the 2wd VSV is Blue-White. (I don't know what the connector-shell colors should be.)

These wires run directly back to the ADD relay, which is a double-throw relay. Based on your testing, the relay is shot, or you have a wiring problem (in both wires; so more likely a bad relay). My manual shows the relay behind the instrument panel, but that's not too helpful. If you can hear yours, that's how I'd find it.

As RJR hints, the 4wd indicator light is powered by a switch in the differential, so it positively indicates a shift. Since you're not even getting the voltage switching at the VSVs, the indicator light is just confirming that the differential is not engaging.

gfrench

Bad relay. Now to find the little bugger!

gfrench

Might it be the little box marked "Computer 4WD Control"? It seems to be where the clicking is coming from when I push the 4WD button. It sure doesn't look like a relay.

RJR

On the wiring diagram I have for the A/T (attached), there are a lot of switches, but only one relay that I can see. On my truck ('94, M/T) the ADD relay is silk-screened "horn relay" on the outside, so don't be fooled by the label. (I remember it as being orange, and maybe a bit more than one inch long.) Listening for it is the best way to find it.

I agree with scope, if the ADD relay is clicking but the voltage isn't switching, something's wrong there. The relay simply takes 12V and applies it to one of the two vacuum solenoids.

gfrench

I didn't find any other relays near where the click noise was coming from other than the box that says 4wd computer 4wd control. It has a wire harness with a bunch of wires and a connector.

Looks expensive.