Chosen Solution
The fan on my 24” iMac starting running at full speed yesterday. I ran Apple Hardware Test and came up with the following error. 4SNS/1/40000001 : TGOD- 1.000 This appears to be an overheating graphics card. I opened the iMac up and blew out all the dust and reassembled. I turned on the computer and before it was fully booted up the fans came on full speed. The computer had been off all night. Is it possible for the graphics card to overheat before the computer is fully booted up from a cold condition? This is an old computer I use to run two old programs that don’t run on my other system. I am running OSX 10.6. Other than the fans running at full speed the system appears to be running fine. Is this a problem that can be fixed? I read somewhere this is a heat sink problem where the cooling fluid has been lost and replacement parts are not available. UPDATE: I just downloaded Macs Fan Control and the CPU is running at 3600 rpm. All the temps look fine except the GPU diode. It is at 1 degree centigrade. Is my diode the problem?
If you took out the logic board then you might have snagged the sensor cable damaging it or forgetting to connect it. If your sure the connection is sound then it could have failed on the most part I find the GPU needs deeper service. It could be a bad heat sink or need new thermal paste and pads. As for the software tool you’re using I don’t have much faith in SMCFanControl as I’ve seen to many problems with it. I find TG Pro is just a better tool to see whats happening.
