LED 1(on the left) connects to an open-collector gear-tooth sensor. The led is used to help set the location of the sensor. It's intended to light up when the sensor is correctly positioned. On the right side, the signal coming out of R6 goes to the MCU.
My diagnosis: The LED will light up when I bring cathode to ground, but I get no output on optoisolator. When I short the LED(remove the led from the circuit) and bring it to ground, The optoisolator works as intended.
Why would the LED cause this issue? Can I provide any other information?