Imac G5 cpu sensor temperature problem

Hello all. My daughter has a 2005 Imac G5 2.0 GHZ (ambient light sensor) with 1.5 GB of ram running 10.5.8. Recently it has been shutting down, well going to sleep on her as well as shutting down quite frequently. A problem my old power book had when it kept "overheating" due to a faulty track pad sensor that i had to remove. Well the powerbook thought it was overheating. I restarted it at first, ran disk utility to repair permissions, no good. Then did the pram reset/ No go. Took it apart and blew any dust out of it i could which was very much. Then i tried the smu which controls fans and such. Still have the problem.

So i decided to add temp monitor to see whats going on. Thats where i noticed the cpu saying its -37 F degrees!! Which is impossible. When u run something like the browser and a game that requires cpu usage, it will spike all over the place. -37, 40, 110..190.160 back to negatives then to..200. etc. Obviously i think the cpu sensor is malfunctioning. Is there any way to replace this or possibly remove? With my powerbook i opened it up and removed the track pad sensor and never had the problem again. Not sure how the cpu is set inside this. On older g4 towers they were socketed and could easily be change/replaced. Thanks in advance!