4WD Not Working...

In addition to the position switches like you tested above, the controller receives signals from both the transfer case actuator limit switch and the ADD actuator limit switch. If the limit switch signals are faulty it can cause faults with the 4WD ECU and prevent the 4WD switch.

The limit switches are located in the actuator itself (the 6 pin connector). Depending on the actuator position the limit switch connects certain pins to ground. I’ll see if I can find a troubleshooting table in the Tacoma FSM that indicates which pins are grounded in each state.

 

Good point. Limit switches can be jumpered from the back of the connector.

 

I wasn't able to find the transfer case actuator test procedures for the tacoma's transfer case. However, I attached one from the 4runner which has a similar pinout and might be helpful. I also found a test procedure for the A.D.D.