Chosen Solution
Well, Thats a good mystery! The ODD sensor is the sensor thats mounted on the optical drive case. Review this IFIXIT guide: iMac Intel 27" EMC 2309 and 2374 Optical Drive Replacement. Jump the Steps 11 & 17 which its connected to the logic board and the sensor its self. The sensor cable Optical Temp Sensor - Apple P/N 922-9229 If the Optical drive fan is defective follow this IFIXIT guide: iMac Intel 27" EMC 2309 and 2374 Optical Drive Fan Replacement and this is the part: Optical Fan - Apple P/N 922-9150 Update (12/03/2017) I think I see what happened here! You forgot to plug the LCD sensor back in. Review this IFIXIT guide: iMac Intel 27" EMC 2309 and 2374 Display Replacement jump down to Step8 is it plugged in?
