Code P1604 and the air pump doesn't kick on or off anymore.

For a couple days when starting my 2013 Tacoma BAJA 4.0 I've noticed the maintenance required light blinking 8 times and now it stays on. Thought it was reminding me to do the oil change until it stayed on (plus I just changed the oil 2k miles ago). I've noticed that the air pump doesn't make any noise anymore when turning the truck on and shutting it off. Took it to the par t's store and read the code with their scanner and it came up with this p1604 code. The truck doesn't have any issues starting at all. Any help would be great. The truck only has 40,568 miles on it.

 

The probable causes for that code cover a wide range of systems/symptoms. BUT since your AIR injection pump seems to be inoperative, I would remedy that issue first.
One of the probable causes for the code is the A/F ratio sensor (wide band O2). That year may use the A/F sensor to monitor and determine how long the AIR pump runs (a running pump will create a lean condition). This is all dependent on whether the engine is HOT or COLD and what the ambient temp is. There could also be another issue keeping the pump from running (other then failure)
Might want to monitor your fuel trims as well to make sure nothing abnormal is going on.