Hi, I have a 1996 4Rnr Limited automatic with 2-4 select switch. I've searched the forum and read threads on this problem, especially from TheDurk and Charchee and done a lot of the tests, but need some clarification. First what I have done so far:
4WD select button continuity check good.
Vacuum from intake manifold 15in Hg at idle (book says 17.7in Hg or > at idle)
Same vacuum at outlet to diff on the unlock VSV when 4WD button disengaged or engaged
No vacuum at outlet to the diff on the lock VSV when 4WD button engaged or disengaged
Both VSVs ohmed at 37 ohms
There is power (11.57v) to unlock VSV when 4WD button disengaged or engaged
There is no power to lock VSV when 4WD button engaged or disengaged. I.E. power and vacuum is not switching between lock and unlock VSVs.
Switched hoses so vacuum was on lock vacuum line to diff but did not hear actuator engage diff and 4WD indicator light did not come on regardless of position of the 4WD button. Same result when I bypassed all VSVs and hooked vacuum line from manifold directly to lock vacuum line to diff.
As I understand the 4WD system operation, pushing in 4WD select button sends power through 4WD 20amp circuit to 4WD ECU enabling it to do its magic. ECU sends signal to TC actuator telling it to engage. When it engages, the 4WD position switch at the TC sends signal back to ECU saying it is engaged. ECU then sends signal to VSVs taking power and vacuum from unlock VSV and transferring power and vacuum to lock VSV which then passes vacuum to differential actuator and locks in the front diff. The actuator movement closes the ADD switch which turns on the 4WD indicator light. The 4WD button must be on for power to get to ADD switch and 4WD light (I'm going to try to attach a diagram from the Toyota repair manual to make sense of what I'v just said).
Now for my questions.
When I bypassed the VSVs and applied vacuum directly to the lock line, I didn't hear any movement of the diff actuator but thought the light would come on if it had moved, but the light didn't. Looking at the diagram I'm trying to attach, it looks like the 4WD position switch on the TC must work in order for power to get through the light and ADD switch to ground. If the 4WD position switch doesn't work, then even bypassing the VSVs still won't turn on the 4WD light even if the diff actuator turns on the ADD switch. Is that correct?
Would there be any problem if I attached a hand vacuum tester to the engage vacuum line to the front diff and applied vacuum to see if the actuator works? Other than noise, is there any visual way of seeing if it actually moves?
Sorry for the long post, but wanted to say what I've tested and see if I understand how it operates. Thanks

 

Forgot to add, that it won't go in to either 4Hi or 4Lo. I'm assuming the 4WD position switch at the TC must be good for either 4Hi or 4Lo. Is that correct?

 

 

Thanks for the response. I was under it last night looking at the TC, switch and wires. Was trying to identify the different switches and looking mostly for any loose wires or obvious issues but didn't see any. As far as jumping the ECU pin 6 to ground, I might try that if I can find the ECU. Near as I can tell it is up under the dash but haven't tried to find it yet. Hoped I could solve the problem without going to the ECU. Would disconnecting the 4WD position switch and jumping the two pins on the connector do the same thing? It would tell the ECU that the TC had actuated to 4WD (even though it hadn't) but then that should let the ECU signal the VSVs and enable the diff to lock and turn on the light?
No, I'm not in PHX. Lived in Payson, AZ in the White Mtns when I bought the 4Rnr used, but have lived in NE Wyoming for the last 12 years.

 

 

I'll give it a try this weekend and let you know how it turns out. Appreciate the reminder on rotating the axles too, I'd forgotten about that.

 

Just finished checking. Looks like a 4WD position switch on the TC at the actuator is bad. Disconnected connector from switch and checked connector with key off -- no power. Turned key on with 2-4 4WD switch off and had power, which confused me since thought wouldn't have power there until 2-4 4WD switch was on. Had power when switch was on too. So checked the VSVs and power had switched from unlock VSV to lock VSV. So, then jumped the connector bypassing the 4WD position switch, started the car, put in 4WD moved it about a foot and 4WD light came on. Drive shaft to front diff was also locked and when I tried to turn it I could hear the movement in the TC case as it hit its limits. So, I'm pretty convinced that is the problem. Do you happen to know the part number for that switch or a good place to get one on-line? Thanks again for the help