2001 tacoma double cab. 4x4 not working

New member, sorry if this post is kinda long. This Truck is automatic with the electric (No vacuum) style T/Case and front differential ADD and was purchased with 117,000 miles. Had been sitting for some time due to rusty frame issue. Has push button 4x4 system with just High and Low T/Case shifter. It Was stuck in 4x4 with no 4x4 dash light and it has check engine lite on. Transfer case shifts between H and L with no problem. Since I completed safety cap frame repair I have moved on to the 4x4 issue.
Seems like there are several different variations of the 4x4 system made by toyota. Vacum style; lever with button like mine; J shifter style , dash knob shifter in later models etc. Lots of threads on this topic but on many I not sure if the discussions always relate to the system I have.

So far,
-Fuse in side cabin is good and has power. Don't see 4x4 fuse in engine bay.
-I've checked continuity on switch on T case shift lever- It was good.
-All 3 switches on transfer case checked out continuity OK
-Had ADD actuator apart- It was clean inside appears to not have problems
has 1 wire with 12 volts coming in to it.
-Had Transfer case actuator apart. Looked good inside also with no obvious issues.
Has 2 wires with 12volts coming to it

Full disclosure, I had taken both actuators apart while stuck in 4x4. Think I have gear rotor rotation set up properly but not 100% sure.

Question -
1. IS there a relay on this 4x4 system? if so, where is it ?

2. IS there an ECM for 4x4 or does it just come from main truck computer? Where is computer(s) located? I've read somewhere about it being behind glove box

3. There is no power coming in to the 4x4 button on T/Case shift lever. One side of wire goes to ground until switch is activated. Assume there should not be 12 volts coming to 4x4 button on shifter to start the 4x4 process this switch just completes the ground?

4. Anybody have a way to bench test the ADD and transfer case actuator?

5 Anybody know for sure how to time the rotors on T/C and ADD actuators ?

6. IF light in dash is burn out, does this shut system down? How can I test it.

I use 4x4 often so it needs to be reliable.

Any help is greatly appreciated

 

@Empty_Lord

 

I don't have the answers but just confirming that I believe Toyota generally puts the switches on the ground side of the circuit, like you mentioned.
So the transfer case is engaged without the light being on in the dash for it?
What DTC do you have for the MIL that's on?
Do you have the FSM? For my cruisers the info on the actuators was all in there. I'd imagine the taco FSM has all that too.

 

2001 4wd system will not be vacuum assist.

Is your Tacoma a TRD with rear 8" elocker or non-TRD with the 8.4" rearend? The 4wd is controlled by a computer regardless. Elocker rear is located by the driver kick panel and non-TRD 4wd computer is located under and inside the ash tray / coin holder area, next the double 12v plug.

 

Cruiser guy, the TC was engaged without 4x4 light on. IT is still engaged as I can't spin front driveshaft. Took off ADD actuator on front diff and inside differential was good. axel Collar slides free. Dumb question maybe:
-DTC? MIL? Are referring the check engine light? I don't know. I don't have a scan tool and it is stuck in shop. Might need to call friend to make house call. It is possible that may tell me the issue but I don't have much confidence in check engine light stuff from past experience. Muffler was shot and figured it was o2 sensor. Probably worth checking the codes. Assumed I could track down the 4x4 issue pretty quick but ?

O2 hilux, Truck is a TRD with locking rear differential. rear diff locker did work (lite came on) when I tried it prior to frame repair but it was stuck in 4x4 at that time. Figured it was something simple Famous last words!. Might be in over my head LOL.

I had battery disconnected through the welding project.

I do not have Factory service manual but Im seeing it in my future
to get out of this jam. Looking forward to driving this thing but pretty much stumped and stuck in my shop at this stage! Hope it is not a gizmo inside transfer case (assume there must be something in there to slide a collar/shaft to lock in 4x4)?

This truck was probably rarely locked in 4x4 or in the mud or hauled much in its life. Was a city truck and has a camper shell and carpeted bed.

 

Hate to say it, but a buddy had all the issue associated with 4wd electrical, lol. Burnt 4wd computer (swap), TC actuator will not lock to 4wd (swap), front diff actuator with not engage (swap). After all said and done, 4wd working again. What a headache...

 

I’ll see what I can dig up after work

 

We actually have a really good group here in this first gen Tacoma forum. I know there are a couple master techs and plenty of enthusiasts that could double as a master tech. I guess I'm saying don't give up on it yet! Get yourself the digital version of the FSM, I think @mechanicjon knows how to get these. Something like this I'd prolly be a little lost on where to start and going off of the FSM and the suggestions from the group here.

 

thanks guys. I'm surely working off fairly shallow intuition here at this point when it comes to these controls.

I see with key on
at front ADD plug I have only pin 3 with 12 volts (Looking at with connector latch on top from Right to Left)
At T/C plug I have pin 3 and 6 with 12 volts ( same view)
No change when pressing 4x4 button.

My understanding is the button should activate different pins to move motor in reverse directions. Wonder if front ADD should have 2 pins powered also? Seems like signal from a relay (or ECM) is not switching power to pins.
Looked behind glove box and there is a ECM looking box there. Did not see anything like that behind ash tray just peeking up from floorboards

 

Just throwing out ideas, could the transfer case plug/switch also be sending 12V to the dash for the 4x4 engaged bulb?

 

I believe you can also power the actuators directly off of a car battery, IIRC. If you wanted to see them function

 

can you explain which pins to touch with hot and which to ground? On ADD unit, could only get it to spark on bench test but not sure I'm doing it correctly?

 

I don't know which, I don't have the schematic. I don't have ADD either on my taco. Hopefully someone here has that at hand. On the add actuator there's only three wires?

 

https://cdn.discordapp.com/attachme...6029436428550155/01_Taco_ADD_Control_INSP.pdf
https://cdn.discordapp.com/attachme...9456213082152/01_taco_4WD_Push_Button_EWD.pdf

hope this helps

 

thanks I'll check it out

 

I had this issue and it was the wiring on top of my glove box had come undone.

 

yeah

 

Do you mean that just the connectors came apart above glove box? It seems like something like that could be the case as I'm getting no change on any components when 4x4 button pressed. Probably too easy though but I'll look.

Looking at the subject of testing ADD, I'm confused about how to hook it up to the relay to test as it is cryptic at best or maybe I need to go back to school? IT says use fuel pump relay then shows heater relay? They are probably the same I'm guessing, but I need more dots connected to see what they mean on hooking up the relay to test the ADD. I'll look at the plug again and maybe it will make sense?

 

Correct, my diff breather line had come undone and must have pulled the harness hard enough when I lowered down the differential.

 

Can someone tell me where the 4x4 ECU located is on this truck? Got clove box and back of it out of the way. Don't see any markings on electric boxes there Read somewhere its behind ash tray? There are many forum threads about push button 4x4 system out there that don't apply to my year truck for sure and its hard to tell what truck they are talking about sometimes.

I read where the all electric actuated tacoma 4x4 does not have ADD relay? The info that Empty Lord sent mentioned inspect ADD relay??? but not

Going in circles here!