Model A1311 / Mid 2011 / 2.5 & 2.7 GHz Core i5 or 2.8 GHz Core i7 Processor

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CPU Fan is running full speed with normal temperatures

Hey All-

I just replaced my hard drive with a 3tb and added a ssd behind the optical bay using the kit and cable from OWC. Everything seemed to go fine and i've been able to re-install the OS.

However, now i've noticed the CPU fan only is running full blast, but the temperature sensors seem low. I've been able to slow it down using Macs Fan Control, but am very curious why this is happening. I could keep using this program, but i'd rather let the OS handle. I have reset smc and pram.

All temperatures are in the mid-30's (C)

Anyone have thoughts here?

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I did a hardware test and found that I am getting 4SNS/1/C00000008: TS2p--124.

From what I've read, this is a skin sensor, causing the CPU to increase. I double checked all my connections and it looks good. I did notice the right ambient sensor cable is a little frayed near the edge, but seems to be connected OK.

Anyone have any other info about this error?

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Chosen Solution

The iMac logic board is pretty picky about the thermal sensors it recognises and will go into general fan panic if in doubt.

Do all your upgrade items have compatible sensors and are they all connected properly? OWC are pretty up to speed on this and may have guidance.

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Adding the SSD didn't require any additional sensors and I did use the sensor cable for the replacement hard drive.

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After this, i took the computer back apart and put the old hard drive in. Still had same problem.

It looked like one of the top temp sensors was touching the case so i got some space around it. Put it all back together with my new drives.

Presto! no more cpu fan going nuts!!!!

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Sounds like the OWC sensor is not doing its job. I would contact OWC to see if they send you a new one.

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If that sensor was not working, wouldn't I be seeing my hard drive fan spin like crazy, not the cpu?

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Have you tried running TG Pro? It will allow you to see the sensors more effectively.

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Hi Dan-

I downloaded this and all my sensors look good..i can see my thermal sensors now, but TG Pro isn't reporting any hard drive sensors. HOwever, Macs Fan Control is showing both my hard drives...

Does this make sense?

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Yes, by default SMART is off which is why the HD's aren't being read. Unless I'm working on a possible HD thermal issue I leave it off as SMART requires an IRQ call which slows your system.

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Have you changed the thermal paste?

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I didn't change the thermal paste as I didn't remove the cpu

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Have you run activity monitor and find out whats using your CPU more?

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I don't have significant cpu usage, and all my temperature readings seem to be within normal range.I think Iain is on the right track, just need to keep digging.

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Chad Predmore will be eternally grateful.
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