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Hello, a couple of days ago I tried to change my Seagate hard drive for another Seagate but with 3Tb and also install a SSD drive in place of the optical drive. I thought everything went quite well during the installation but when I finished it turned out that the CPU fan was going crazy. I checked several posts and seen that other people complained about fans going crazy and it was due to some sensor not working, so I tried several things but none of them with result: Connect the optical drive sensor to the LCD sensor socket to see if that was the problem.Connect the optical drive sensor to the HDD sensor socket.Same as before but also connecting HDD sensor to LCD sensor socket. None of them seemed to work so I ran AHT and I got this results: 4MOT/4/40000003 HDD-14164MOT/4/40000003 HDD-14224MOT/4/40000003 HDD-1426 So I thought that it was worth checking if all fans and connectors were working. I first unplugged the ODD fan and connect it to the HDD fan and it worked fine, did the same connecting it to the CPU fan and seemed to go like crazy, but worked. Finally I decided to unmount the HDD fan and plugged it to the ODD connector and surprisingly it worked. Then I tried to limit the fan max speed via programs like SMCFanControl or SSDFanControl but with no luck, all of them reported that the CPU fan speed was 0rpm and it’s the one going crazy. So.. my problem I’m totally lost. I don’t know if it’s worth buying a new HDD fan and see if it might solve my problem or if I might take the same route as others and hack the CPU fan, or maybe change the logic board… Any ideas?
Apple used a proprietary heat sensor on the hard drive of this machine. Use an OWC In-line Digital Thermal Sensor for iMac 2009-2010 Hard Drive Upgrade to cure this problem OWC In-line Digital Thermal Sensor for iMac Late 2009 - Mid 2010 HDD or SSD Drive Upgrade
I would check to see if you lost a resistor in the process. Seems common that if you have a CPU fan which reads 0 rpm but seems to be going full blast, there’s likely an issue with the circuitry on the logic board. What a few people have found in another thread is that there’s a 47KΩ resistor which is missing near the power button connector. If you have one missing from there, all you need is a new resistor and your Mac will function CORRECTLY because it knows the fan speed. Link: CPU Fan runs at full speed.
You’re right you have a sensor issue. The sensor reports to the EFI that it can’t detect/control the FAN so the EFI runs the fan at full throttle (by default in scenarios like this) to keep you from cooking your CPU. I don’t know if you damaged the connector, blew up the sensor but the error is basically saying it believes your FAN MOTOR (4MOT) for the HD (HDD) is out of spec. and the amount it’s wrong is the last set of numbers in RPM (I suspect too slow - hence kicking it into overdrive). MAYBE you need an EFI update to run that drive? What is it’s SATA Speed (your bus is 3Gb/s Max) Have you tried an SMC reset? If this answer is acceptable please remember to return and mark it.
I’m having the same issue, although its not immediate and istat shows ~1400 RPM before the issue occurs. then when it occurs, the fan goes to full speed and shows 0 RPM. i am not knocking my iMac at all. it just seems to happen on its own during use
You might be able to use SSD fan control and set it for manual 3000 RPM - it’s a coping mechanism until the problem can be solved.
