ADD issues

Hey gents,
So in the past my Tacoma was getting stuck in 4x4. After disengaging manually by removing the transfer case actuator and pushing it back into 2WD and putting a battery on the Front ADD a few times, I replace the transfer case actuator. I replaced this due to the red dial not providing the correct reading unless the dial had preasure on it to make it connect. After the new actuator was installed, the truck has not had 4wd. Currently the trucks actuator moves into 4hi but it does not engage the front ADD, but can be manually locked using a battery. After getting stuck multiple times over the past month in the woods I’m ready to fix this 2WD princess. Does anyone have any idea of what could be going on? Thank you

 

I’m having the same issue, I took the actuator off, shifted it to 2wd manually and then timed it by the video I watched. When I get it back together and try it the 4wd indicator just blinks. It’s “locked in” and pulls the front tires but the indicator isn’t showing that it’s in actual 4wd. Any suggestions?

 

When you say locked in, do you mean both the transfer case is confirmed to be successfully shifting to 4WD and the ADD is confirmed to have engaged the right wheel?

Those two both provide inputs confirming their position before the 4WD ECU will turn on the light. You probably still have a problem somewhere with one or the other.

 

If I put it in 4hi, hold the brake it won’t burn a tire so I assume the ADD is working. I changed the ADD.

 

Usually it is always the the ADD that goes bad, or will go bad anyways. New dorman ADDs come completely soldered, I did open it up to solder it, only needed to add dielectric grease everywhere before installing it.

If it is problems with 4LO, then it is the transfercase actuator 99% of the time.


ADD is always the first and last to engage/disengage.
Shifting process from 2wd is; ADD --> 4Hi --> 4Lo

 

That’s backwards. The transfer case has to engage first because when driving in 2WD, the intermediate shaft and the right cv are spinning opposite of each other. Transfer case shifts first in order to spin up the driveshaft using the synchro in the transfer case. Add engages afterwards. Contrary, going from 4Hi back to 2WD will disengage the ADD first, then shift the tcase.

 

I think that the ADD is working like it should because if the add didn’t engage then it would still technically be in 2wd correct?

 

Well, it takes both to be engaged to truly get 4wd. I got a little stumped when you provided that update. If it can’t peel out a tire then I wonder if you have a bad indicator in one of the actuators not providing the proper signal to the ECU so it will make the light solid.

 

That’s what I was guessing but I’m not sure. I ordered a new Aisin today I bought one of Amazon just to try it and it immediately threw the switch failure code when I hooked it up. I thought maybe it was a timing issues with the gears but I’ve literally took it apart and put it back together over a dozen times. I’m stumped also.

 

At this point you probably need to jack up the front and test out the driveshaft to make sure it truly locks in at the tcase and then check the ADD to make sure it locked in and that the right wheel spins the diff.

If you have those 2 confirmations, then you know it’s either the sensors reporting to the ECU improperly or it’s the ECU that went bad and isn’t properly sending the right light indicator signal.

 

The sensors in ADD or the limits in the transfer case actuator?

 

Could be any. The transfer actuator has 2 switches for reporting position. One for 4L and one for 4WD. Those also tie to other systems like the TRAC system from the brake module, etc.

The ADD actuator uses all limit switches but the one called “ADD” is the one that reports the data that the shift is complete. Technically all the limits do that but “ADD” is the one that is equivalent to the position switches in the transfer case actuator.

For the ECU to believe you’re in 4WD, I believe you need the ADD circuit and the 4WD circuit on the two actuators grounded. And then I think the L4 circuit receiving ground is what allows the ECU to know you’re in 4L.

The ECU definitely still monitors the all of the limit switches as well, but I don’t think it uses them in the logic to control the shift light. But, I suppose it’s possible. I did a lot of testing but it’s hard to say for certain because I wasn’t specifically looking for that.

 

Check this out. This may help you with troubleshooting. Part 2 and 3
https://youtu.be/3SfKkG4Il7g?si=aXbUsd7UOGLMBH-B

 

Here is some information on limit switches.

I would start with the harness at transfer and ADD. Follow colors in diagram and pin # for each connector.


TL1-T3 are limit switches in transfer







DL1, DL2 ADD's limit switches. ADD is position switch