Hello everyone, new to the forum but not new to tinkering with computers. I have had my Mid-2009 Macbook Pro 15.4" with Duo 2.53ghz for the last three+ years and it has been a good computer. The most expensive repair was a top case a while back for $250. For the most part I was able to do all other repairs myself (SuperDrive repair/upgrade to SSD/replace SuperDrive with a HDD caddy). Up until recently it functioned perfectly. Now it still does except the fan. A week ago the fan just out of the blue, spun up to its max of 5,700rpm. No reason. Temperature of the CPU is 98F-100F using smcFanControl. Performed an AHT and it returned the following problem: 4SNS/1/40000000: TC0D- 128.000 I accidentally interpreted this to be a palm rest temperature sensor and replaced the trackpad today. Well, now the fan is randomly spinning up and down from 2000-5700. It is extremely annoying and other than the noise, the computer functions just fine. I would like to get it silent again. Any ideas what can be causing this odd occurrence? From what I have read, it is a CPU temp sensor, but my sensor readout is not fluctuating. I have reset the SMC and PRAM multiple times, nothing helps. Is there something loose or is something much harder to fix happening? Thanks!