4WD not working...Help!

Hi,
So I have an 06 tundra and I got stuck the other day and found out my 4WD is not working. The actuator for the transfer case is working perfectly and engages the drive shaft for 4hi and 4lo. The switches in the dash are lighting up correctly. Solid light when I turn it on and it turns off properly. The 4lo light/switch also works properly. Opened up the ADD, cleaned up the points and every thing inside of there was in great shape. Bench tested the motor on the ADD and the motor runs perfectly. I then manually turned the ADD actuator and it successfully engaged the 4WD. From everything I've seen so far the ADD seems to be fine. Hears where I'm a little unclear on diagnostics, I checked the leads and wiring harness from the ADD. They look to be in perfect condition from the outside. I checked them with the multimeter and Im getting juice in 3 or 4 of the six points inside the connector. I'm assuming that is normal. There is a vacuum hose going to the ADD and it seems to be in good condition. In the other forums I've read people were saying that its not really a vacuum hose but just a vent hose. That would mean its pretty inconsequential.

What am I missing!
Any help would be much appreciated! Thank you in advance.

 

No I already had the 4wd on and was under the impression it was working

 

I’ll try that, the only thing that has me stumped though is that when I hit the 4hi button I can clearly hear the actuator motor and “clunck” on the transfer case. There is absolutely no noise coming from the ADD. This makes me think it’s not getting power.

 

Okay I had read something before about the ecu, do you know where the 4x4 ecu is located?

 

Late model Tundra, Tacoma, FJ Cruiser and 4Runners equipped with part-time 4WD are, especially at higher mileage, more susceptible to 4WD failure than their older brethren. In a similar vein as the 4Runner we repaired recently that had a failed transfer case actuator, CARspec was tasked with a Toyota Tundra that wouldn’t complete the engagement of 4WD from 2WD – the select button would only blink. The technician noted while the vehicle would engage 4WD high (as in all 4 tires were powered), the system wouldn’t complete it’s operation and prohibited a 4WD low selection (it didn’t think it was in 4WD proper)

After checking the transfer case actuator and switches for functionality, the technician noted the final completion switch inside the front Automatic Disconnecting Differential (A.D.D.) had excessive electrical resistance when it was normally supposed to be resistance free (when the switch was closed it registered too much resistance).

The A.D.D. system on late model Toyota trucks and SUVS is used to disconnect the front axles from the differential. This increases fuel economy because the front drive shaft and axles aren’t subjected to the same rotational drag they would be if they were still connected. A small electric motor inside the front differential engages a splined collar that links everything up inside the front differential. Inside this failed A.D.D. unit the final switch that indicated a complete engagement had failed. The 4WD module, not knowing if the A.D.D. was done working, kept waiting for a switch signal that would never come.

Here’s the A.D.D. opened up:


ADD Actuator

The engagement fork fits over a splined collar inside the front differential. The small electric motor, using the larger sprocket behind the spring, winds the engagement fork into place, while wiper switches (not pictured but behind the sprocket and spring) let the 4WD module know what’s going on.

The repair for this was straightforward – replace the A.D.D. It’s important you properly reseal the differential with FIPG (the orange in the above photo, similar to this post about a leaking cooling system due to poor FIPG use), but otherwise the repair is a simple job with hand tools and some maneuvering.

As Minneapolis’s independent Toyota and Lexus repair specialist, we are able to diagnose and repair the above in only a few hours, at considerable cost savings vs. the dealership while offering the same technical prowess you’d expect from former factory-trained mechanics. If you are having 4WD issues with your Toyota or Lexus, don’t hesitate to call us at (952)426-4798 to make an appointment today

 

Checked ECU wasn’t that either...