1996 Limited won’t engage 4x4-suspected electrical problem

[jnowlin]

I had to rebuild my front diff due to pinion gear walk, and my Runner was down for several months. After finally getting it all back together, the 4x4 is not engaging. I have long had the wire unplugged on my transfer case that has previously always allowed the button on my transfer case to be used as a 4x4 on/off switch, but now I’m getting no green light indicating it’s in 4x4, and it’s definitely not pulling in the front. My buddy has checked the front actuator, the front diff indicator sensor, the sensor in the ADD tube, the VSVs, and the 4x4 actuator on the transfer case with a power probe, and all appear to be functioning properly. There is vacuum to the VSVs, but for whatever reason, they won’t swap vacuum. At this point, we think it’s most likely an electrical issue. Has anyone else ran into this problem, and if so, what was the fix?

 

[Bad Luck]

Have you tried applied power and ground to the VSV to see if it will switch or are you depending on the vehicle to apply power and ground to make it switch?

 

[toyotaspeed90]

I would check the 4wd switch in the transfercase first. These type.of switches can get stuck if not used and if the 4wd computer doesn't see that the transfercase is in 4wd it won't engage the ADD for the front end.

 

[jnowlin]

Have you tried applied power and ground to the VSV to see if it will switch or are you depending on the vehicle to apply power and ground to make it switch?

Yes, we applied power and ground to the VSV with a power probe to see if it would switch and it didn’t.

 

[jnowlin]

I would check the 4wd switch in the transfercase first. These type.of switches can get stuck if not used and if the 4wd computer doesn't see that the transfercase is in 4wd it won't engage the ADD for the front end.

No, we have not replaced the transfer case switch, but it isn’t switching on with the button on the transfer case shifter either.

 

[Bad Luck]

Yes, we applied power and ground to the VSV with a power probe to see if it would switch and it didn’t.

If your VSV isn't switching vacuum when you apply the appropriate power and ground then the VSV is your problem. Here's the FSM excerpt for testing the VSV.

 

[toyotaspeed90]

The 4WD button you push on the transfercase is simply lopped to ground when pushed - start simple and see what happens. You don't have to replace switches so much as just test the wiring first.

Jumper the 4wd button wires with key on - is the transfercase electric motor trying to engage 4wd?

If so, do you have ground at the 4wd computer from the transfercase (if the electric motor is successful to move the transfercase into 4wd) for the 4wd switch (the internal 4wd switch).

The VSVs (ADD) are controlled by the 4wd computer in a limited and the 4wd button and the 4wd internal switch have to be at ground before it tries to activate ADD.

 

[jnowlin]

If your VSV isn't switching vacuum when you apply the appropriate power and ground then the VSV is your problem. Here's the FSM excerpt for testing the VSV.

The VSV switches close and open when bench tested.

 

[jnowlin]

The 4WD button you push on the transfercase is simply lopped to ground when pushed - start simple and see what happens. You don't have to replace switches so much as just test the wiring first.

Jumper the 4wd button wires with key on - is the transfercase electric motor trying to engage 4wd?

If so, do you have ground at the 4wd computer from the transfercase (if the electric motor is successful to move the transfercase into 4wd) for the 4wd switch (the internal 4wd switch).

The VSVs (ADD) are controlled by the 4wd computer in a limited and the 4wd button and the 4wd internal switch have to be at ground before it tries to activate ADD.

The switch tested good. I don’t know otherwise because we haven’t yet looped the wires at the switch with key on engine off.