apex pm2 question

[Slyguy00]

Im trying to hook up my salinity probe and pm2 module to my apex and im having some issues. I have watched the brs video multiple times on how to calibrate and set it up but im having no luck. It does not seem to matter if the probe is plugged in or not it is giving me a reading of 7.6. Even uncalibrated it should read alot closer than that. It almost seems like my apex isnt recognizing the pm2. Also when i try and calibrate it and then save it says calibration failed and it is returning to factory settings. Has anybody had this problem before or know how to fix it? Please help.