No power out of 4WD ECU

Hello,
First time poster. There may be other threads on this, but I can't seem to find the exact problem.
My 4WD light has been blinking for months after unsuccessfully shifting into 4hi. I know the ADD actuator is working because I took it out, tested the motors, and soldered the connections. This didn't fix the problem.
I have it at a shop now and they're saying they have the correct voltage coming into the ECU, but nothing coming out. Logically it would seem that the ECU is bad, but I see that ECUs don't often go bad.
Any insight?
Please and thank you!

 

Welcome to the forum. They should look for chewed wires.

 

Thanks
They were looking for any shorts, but came up with the proper voltage through the wires, just nothing after the ECU. Am I correct in thinking that nothing down stream of the ECU could cause this?

 

Unfortunately not.

 

In a 3rd gen, the 4wd Ecu only outputs power to the actuators if the ECU decides the actuators are in a valid position, and it wants them into a different position. If the feedback from the actuators shows invalid data, the ECU will not output power, and will failsafe

I have not seen a bad ECU. It is very possible that you have a bad ADD, even though you worked on it, unless you verified the feedback wiper signals.

What did you find in the ADD, did it look bad?

To troubleshoot, my opinion is there are two major methods to start with:
Verify the feedback signals from the ADD and Transfer Actuators and motor resistance of the actuators.
Use Techstream to provide data on the actuator feedback.

Third option, try to use evidence of which driveshaft is operating while shifting into and out of 4wd after power cycling the truck after every motion.
Fourth option, throw parts at it.
Fifth option, use a divining rod https://en.wikipedia.org/wiki/Dowsing.

See the thread below for more details on data I recommend as useful for troubleshooting a 3rd gen.
https://www.tacomaworld.com/threads/4wd-actuator-troubleshooting-transfer-case-and-add.578262/

Let us know if you pick a route and want some help, but you have to decide what type of troubleshooting you are comfortable with.

 

Thanks for the troubleshooting advice; I'm a novice, especially when it comes to troubleshooting electrical components. I ended up taking it to a dealer; it was in fact the ADD. I think I jumped past this conclusion because it looked great when I opened it up and another dealership had replaced it less than two years ago.
Anyway, the ADD does seem to be the primary culprit so best to confirm that's good before going any further. Thanks again.

 

Thanks for coming back and giving an update.
It helps increase our team knowledge, much appreciated.