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I have a mid 2011 27” Imac with an SSD which has been installed for the last 6 months without problem. Two days ago whilst working on the Imac the screen went to a blank light grey screen. I tried rebooting the machine but half way through the boot timer the screen drops to the same blank light grey screen and will try to reboot on its own accord, which inevitably returns back to the blank screen half way through the load process. I have managed to get into the hardware diagnostic which gave the fault code 4SNS/1/40000000: TH00-9.000 Could anyone please help? Many thanks.
Sounds like a fan error. When you did your hard drive upgrade, did you use the OWC thermal sensor? https://eshop.macsales.com/item/OWC/DIDI…
