No juice to injector 4

Diagnostic fault codes never say to replace parts or that one is bad. They only indicate the circuit that needs further diagnosis or the unacceptable operating condition. When a part is referenced in a code, it is actually the cause of that code only about half of the time. You also have to consider corroded connector terminals and cut or rubbed-through wires.

Three-wire magnetic position sensors usually develop a square-wave signal that bounces between 0 and 5 volts. I'm not sure what it takes to set the code you have. Other sensor signal voltages are usually limited to a range of 0.5 to 4.5 volts. 0 volts is not an acceptable voltage and is what it takes to set the code you have. There's two ways to look at that signal. One is with an oscilloscope which is built into a lot of newer scanners. The other is to view the sensor on a scanner's screen, then look at whether it is listed as "No" or "present". That is how it's done with my Chrysler scanner. That scanner will work on other brands of vehicles but with reduced functionality.

The best I can suggest is to measure the three voltages by back-probing the sensor's connector. The voltages will only be accurate when the sensor is plugged in. You should find 5.0 volts on the feed wire, and 0.2 volts on the ground wire. If those are right, measure on the signal wire. Expect to see that voltage change if you turn the engine a little by hand.

If the signal voltage stays at 0 volts before condemning the sensor, check the 5.0 volt feed terminal to be sure it's not spread and failing to make contact with the mating pin.