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Old Jun 27, 2013, 02:02 PM   #26
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Join Date: Jun 2013
Given the recent bump, I figured this thread was as good as any to respond to.

I just picked up an Early 2008 24" iMac 3.06 C2D. smcFanControl tells me that the ODD fan is running at full speed all of the time. I did an SMC reset and a PRAM reset to no avail.

I ran the Apple Hardware Test and got this code:
4SNS/1/40000000: T00P - 128.000
Some Googling tells me this is sensor-related. I believe my iMac uses this sensor and iFixit has a replacement guide for the same vintage 20" iMacs here. Is this process applicable to my 24" as well?

Does it seem like replacing this sensor should cure my issues? I see several temperature readouts in iStat but nothing seems out of line or failed, and there isn't a sensor listed for the optical drive. Am I missing something?

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Old Jul 8, 2013, 06:57 PM   #27
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Join Date: Jun 2013
In case anyone finds this in the future, the optical drive temp sensor fixed my problem. Instead of paying $15 for the suction cups from iFixit, I found identical units at my local home improvement store for $2. I picked up a driver/bit set containing all of the torx bits I needed for about $6. I got part number 922-8222 from It took nine days after ordering for the part to come in, but it did the job.

Before, as soon as the computer was turned on, the ODD temp sensor would climb to 127 degC and then blank out according to Temperature Monitor. Now it's holding steady at around 26 degC and the ODD fan is at 700rpm.
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