Toyota ADD troubleshooting

Tonkaman

Tonkaman

Well-Known Member
Location
West Jordan
Recently my 4wd decided to stop working, leaving me to travel the maze in 2wd. I have read endless threads about the Automatic Differential Disconnect (ADD) being problematic and prone to failure. I am getting a bit confused with the entire electrical process between the shifter switch and the ADD itself. I haven't found any great diagrams of the electric only actuator, just the electric/vacuum type. Perhaps some of you can help me understand and work through the process of elimination.

My truck is a 2004 Tacoma 3.4 liter auto and J-shift transfer case. When I shift into 4wd the dash light does not illuminate. I can hear the 4wd relay clicking with the shifter moving from 2wd to 4wd. With the 4-lo engaged I do get low range but still just 2wd.

If I understand correctly, the shifter pushes a switch which then switches a relay turning on power the ADD motor. The motor drives a gear that slides a sleeve from the passenger axle shaft onto the driver shaft locking the two together. Is that right? What is supposed to make the 4wd light come on and blink? Is it the sensor on the t-case?

I pulled the plug from the ADD and tested the pins for power. There are 6 pins total and pins 2,3 both had 12v while in 2wd. I repeated in 4wd and had 12v at 3 and 11.5v at pin 6. This leads me to believe that the problem is inside the ADD motor and probably has a bad contact inside.

I don't want to order a new motor unless I'm sure that's the problem since they are expensive. I also have to drain duff fluid to pull it out and inspect it so I'd rather not since its my DD. Please help me understand this a bit better so I'm not wasting time and money. Any further insight would be greatly appreciated, thanks
 
No vacuum lines on this year, it's strictly electrical. That's half the trouble in finding is all the threads on the actuators seem to be for the vacuum type
 
It's a pretty in depth system to diagnose. Most common things are shift rod position switches on the t/case(cheap and easy fix) or the add actuator it's self. You can jump the switches on the t/case one at a time and see if it engages the actuator with it running in the air. If you jump one and it engages that's the bad switch. Or tap the a.d.d. actuator with it running in the air and it engages while tapping it the actuator is sticking. you can also pull the 4wd ECM and check the position of all the switches and actuators to determine which one is "out of place" I see these systems stump people a lot. I'll try to get the diagram steps posted for you tomorrow.

From what you have said your understanding is pretty spot on. The switch tells the ECM you want 4wd, then the ECM engages the t/case to 4wd and makes the lights flash on the dash (front driveline is now spinning) the t/case shift rod position switch tells the ECM it's new position, then the ECM engages the a.d.d. In the diff for 4wd, Then the a.d.d. Reports it's position and the light eliminates on the dash as you hear a click or pop form the drivetrain and your lights go solid as it's now fully engaged. Revers order for 2wd. 4 low is just one rod moving for low and 1 position switch to confirm it and set the light on the dash.

I would start by jumping the switches on the t/case and seeing if it will engage with one of them jumped.

If you think it may be the a.d.d. Actuator try repairing it. The contact points of the motor arc and create poor contact (which is why tapping it while it's trying to engage and running in the air may make it pop into place, like tapping a starter while it's trying to crank) Open it up carefully and solder the polls together. Here is a link to a DIY about it. Just an idea that could save $$ rather then replacing the actuator. http://www.tacomaworld.com/forum/2nd-gen-tacomas/263525-how-trouble-shoot-4x4-actuator.html
 
Last edited:
gorillaxj said:
It's a pretty in depth system to diagnose. Most common things are shift rod position switches on the t/case(cheap and easy fix) or the add actuator it's self. You can jump the switches on the t/case one at a time and see if it engages the actuator with it running in the air. If you jump one and it engages that's the bad switch. Or tap the a.d.d. actuator with it running in the air and it engages while tapping it the actuator is sticking. you can also pull the 4wd ECM and check the position of all the switches and actuators to determine which one is "out of place" I see these systems stump people a lot. I'll try to get the diagram steps posted for you tomorrow.

From what you have said your understanding is pretty spot on. The switch tells the ECM you want 4wd, then the ECM engages the t/case to 4wd and makes the lights flash on the dash (front driveline is now spinning) the t/case shift rod position switch tells the ECM it's new position, then the ECM engages the a.d.d. In the diff for 4wd, Then the a.d.d. Reports it's position and the light eliminates on the dash as you hear a click or pop form the drivetrain and your lights go solid as it's now fully engaged. Revers order for 2wd. 4 low is just one rod moving for low and 1 position switch to confirm it and set the light on the dash.

I would start by jumping the switches on the t/case and seeing if it will engage with one of them jumped.

If you think it may be the a.d.d. Actuator try repairing it. The contact points of the motor arc and create poor contact (which is why tapping it while it's trying to engage and running in the air may make it pop into place, like tapping a starter while it's trying to crank) Open it up carefully and solder the polls together. Here is a link to a DIY about it. Just an idea that could save $$ rather then replacing the actuator. http://www.tacomaworld.com/forum/2nd-gen-tacomas/263525-how-trouble-shoot-4x4-actuator.html
Click to expand...

Thank you so much!!! That is the clearest explanation I have gotten from any resources I've found including two other forums
 
I finally got enough time to get this fixed. The hardest part of this whole repair was getting a thorough education on the entire 4wd system. After carefully troubleshooting each sensor individually I decided it had to be the actuator itself. The job was very simple: Drain the diff, remove 4 bolts, pull the actuator out. Upon inspection everything seemed a bit rough. There was corrosion on the gears from water and the motors brushes were really worn down. I tried to bench test the motor but with so many contacts I wasn't even confident I knew how. The inside is pretty much a circuit board that makes/loses contact as the gears rotate.

After determining I couldn't get the motor to spin despite all efforts I shelled out nearly $400 for a new unit. Installation was a PITA since the fork has to line up perfectly with the collar inside the diff. No big deal except the only angle I had to work with caused the fork to push the collar over out of alignment every time I slid it into place. After a series of cuss words and a few new silicon applications it was in! With the truck up on stands I engaged 4wd and heard the sweet sound of my actuator engaging, it was glorious!

This is the actuator
ImageUploadedByTapatalk1417312772.601862.jpg
ImageUploadedByTapatalk1417312802.704604.jpg

With the controls removed
ImageUploadedByTapatalk1417312840.697104.jpg

Contacts on the gear
ImageUploadedByTapatalk1417312875.554003.jpg

The 'circuit' that the contacts engage. Also notice the small gear, this was highly corroded and in a pool of moisture/rust
ImageUploadedByTapatalk1417312919.978922.jpg
ImageUploadedByTapatalk1417312969.775576.jpg

Exploded view of motor
ImageUploadedByTapatalk1417312996.679822.jpg

Armature
ImageUploadedByTapatalk1417313028.066019.jpg
ImageUploadedByTapatalk1417313049.699317.jpg

Burnt up brushes
ImageUploadedByTapatalk1417313072.911989.jpg
 
Good job! The old actuator looks toasty for sure. Not that it's a viable option now, but can the ADD system be replaced with a solid axle shaft and locking hubs?
 
bryson said:
Good job! The old actuator looks toasty for sure. Not that it's a viable option now, but can the ADD system be replaced with a solid axle shaft and locking hubs?
Click to expand...

I've read several people just spinning the actuator by hand into the locked position and then jamming the gears so they can't unlock. Then they just put on manual hubs and its a "cheap" fix. Sounds more like a quick fix to get off the trail, but tacomas never really need 4wd [emoji6]
 
cruiseroutfit said:
Congrats on the fix. It looks like it spent some time in a moist environment?
Click to expand...

The corrosion alone didn't seem severe enough to cause the failure. I fact the inside only had a few actual drops of water. I think it was just burnt up brushes. Funny most actuators fail because of too little use, and mine may have failed from too much use
 
Wouldnt a manual hub conversion cost more than the actuator you bought?
Seems like a silly way to fix an easy problem.
 
With junkyard parts it could be cost effective, but new parts would be more like a grand. I think the real attraction is not being 10 hours down a dirt road and realizing your 4wd doesn't work....
 
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