AHT error: 4MOT/4/40000003: HDD-1218

Troubleshooting imac 27" 2011 3.7gh 12gb ram, with 2 ssd 1 hdd.

I ran AHT And got the error 4MOT/4/40000003: HDD-1218, also ran ext test and got 4MOT/4/40000003: HDD-1231.

Internet suggests fan motor issue or thermal sensor. Question is which is it? is it fixable and is it the issue im actually experienceing?

As i am experiencing no luck booting other than one instance booting in Single user mode : CMD S . loaded perfect and fast, airdrop not working, produced a crash report. downloaded ssd fan control and installed successfully. tried restarting in same mode , loads verbose screen. loaded using command exit. Loaded fast and then a black screen.

I imagine the error is because the SSD Fan control does not load until user has logged in.

Worked for years no issue and no slow down. have just done fresh install of osx high sierra....