The tool reset did in fact work

In working on a 2000 VF 6 Haas mill. I'm getting a low air pressure fault. PS is good,contacts are closed. Pressure is good also. From the print the wire goes to P19 There's something else plugged in there...it's on the large card ,lower left in back electrical panel. The print shows an opt o coupler in use..but I couldn't find a user replaceable device on the control board. I could use some help!! Mike S