iMac 2011: Fans at Max Speed, CPU Throttled to 1.7 GHz, GPU Underperforming—Need Help!

[GidroGen]

Hello everyone!



I'm experiencing a serious issue with my 2011 27" iMac and can't seem to find a solution. Here are the main problems:



- All fans are running at maximum speed.

- The CPU is throttled down to 1.7 GHz.

- The GPU is operating at only 20% of its capacity.

- After waking up from sleep mode, everything works normally for about 10 seconds, but then the problems return.



Here's what I've already tried:



- Replaced the CPU with an i7.

- Replaced the logic board.

- Installed new RAM.

- Upgraded the SSD (from a Samsung 840 EVO 500GB to a Samsung 870 EVO 1TB).

- Installed an OWC In-line Digital Thermal Sensor specifically for my model, but it didn't resolve the issue.

- Disconnected the central HDD fan because it was very loud; however, reconnecting it didn't change anything.

- Reinstalled macOS High Sierra.

- Reset NVRAM/PRAM and SMC multiple times.

- Checked all cables and connections; the LCD Proximity sensor appears to be in perfect condition, but temperatures for Hard Drive Proximity and LCD Proximity are not displayed.



I'm using *Macs Fan Control*, *Intel Power Gadget*, and *iStat* for monitoring temperatures, but nothing changes: the CPU remains at 1.7 GHz even under load, and the GPU runs at minimal capacity.



Has anyone encountered a similar issue or have any suggestions on what else I can try? I would really appreciate any advice or help! Thank you!

 

[weckart]

It sounds like it is displaying all the symptoms of not having a HD sensor. Full throttle fans and a throttled CPU. You might want to look at that OWC kit and check it was connected correctly.

 

[GidroGen]

It sounds like it is displaying all the symptoms of not having a HD sensor. Full throttle fans and a throttled CPU. You might want to look at that OWC kit and check it was connected correctly.

I have thoroughly checked the OWC In-line Digital Thermal sensor, and everything appears to be functioning properly. However, for some reason, the system does not recognize it, and I can't resolve this issue at all

 

[weckart]

I have thoroughly checked the OWC In-line Digital Thermal sensor, and everything appears to be functioning properly. However, for some reason, the system does not recognize it, and I can't resolve this issue at all

Did the sensor work fine for a while installed then stop working or has it never functioned properly? You may just have a bad sensor in the latter case. I'm not sure how you can tell that it is functioning properly if the system does not recognise it.

 

[GidroGen]

Did the sensor work fine for a while installed then stop working or has it never functioned properly? You may just have a bad sensor in the latter case. I'm not sure how you can tell that it is functioning properly if the system does not recognise it.

Unfortunately, it has never worked properly. I bought it, installed it, and it didn't change anything. The Hard Drive Proximity temperature was not being displayed and still isn't.

 

[Bigwaff]

Unfortunately, it has never worked properly. I bought it, installed it, and it didn't change anything. The Hard Drive Proximity temperature was not being displayed and still isn't.

Bad sensor.

 

[GidroGen]

Bad sensor.

Maybe, but I don't think there's anything wrong with it. I bought it new from a trusted seller specifically for my model.

 

[weckart]

Maybe, but I don't think there's anything wrong with it. I bought it new from a trusted seller specifically for my model.

I have the same kit in my 2011, which I put in years ago. Worked immediately and I never had a problem with it until yesterday when my 2011 just stopped booting. Another repair to add to the list. I think your sensor is either a dud or something hasn't been inserted properly.

 

[GidroGen]

I have the same kit in my 2011, which I put in years ago. Worked immediately and I never had a problem with it until yesterday when my 2011 just stopped booting. Another repair to add to the list. I think your sensor is either a dud or something hasn't been inserted properly.

I purchased the central HDD fan sensor from a reliable store for $48, and it looks perfect. Yesterday, I disassembled my iMac and carefully reconnected the sensor, ensuring that everything was done correctly. Despite the perfect appearance and proper installation, the computer still does not recognize the sensor.
Could there another issue preventing the system from detecting it?