HP Color Laserjet 3600 shows error 50.9 and 50.1 . It change sometimes 50.9 and sometimes 50.1 . How to solve it?

50.1 Error: (Low fuser temperature)
1. Verify the fuser is installed correctly and fully seated.
2. Check that connector J6007 on the fuser is seated correctly. Replace the connector as necessary.
3. Turn off the printer.
4. Remove the fuser.
5. If there is no conduction in the main thermistor, measure the resistance between fuser connectors J6007LA-1 and J6007LA-3. If the resistance is not 100 kohms to 3 Mohms, replace the fuser.
6. If there is no conduction in the fuser heater, measure the resistance between fuser connectors J6007LAF-1 and J6007-2. If the resistance is not 5 ohms to 1 kohms (100 to 127 V) or 20 ohms to 1 kohms (220 to 240 V), replace the fuser.
7. Upgrade the DC controller firmware.
8. Replace the DC controller PCA.

50.9 Error:(High fuser temperature (subthermistor))
1. Verify the fuser is installed correctly and fully seated.
2. Check that connector J6007 on the fuser is seated correctly. Replace the connector as necessary.
3. Turn off the printer.
4. Remove the fuser.
5. Measure the resistance between fuser connectors J6007LA-2 and J6007LA-3. If the resistance is not 100 kohms to 3 Mohms, replace the fuser.
6. Replace the DC controller PCA.