Wire unit (reference 1image "Light pipe temperature sensor connection") of the temperature sensor is disconnected from the Signal Backplane.

Plug in the wire unit of the temperature sensor into its socket on the Signal Backplane.

Damaged wire unit of the temperature sensor which measures the temperature of the cooling block of the light pipe entrance.

1. Repair the wire unit.

2. If not repairable, replace the whole wire unit and temperature sensor.

Defect temperature sensor on the cooling block of the light pipe entrance.

Replace the temperature sensor.