PowerBook G4 Random Sleep
From Mac Guides
There is a issue with PowerBook G4s mainly 1.67 GHz models which will cause the computer to enter thermal sleep.
Signs of This Issue
Your PowerBook randomly goes to sleep and the console log shows stuff like "Received emergency overtemp warning from PMU. Going to sleep now. Track Pad reporting temperatures above the rest of the computer.
The Track Pad thermal sensor should report temperatures less than the rest of the computer unless you just woke from sleep. Mine is usually 10ºC less than the CPU Top and CPU bottom reading
You can take your PowerBook G4 in for repair. They will most likely replace the Top Case
You can replace the Top Case yourself
You can try unplugging the thermal sensor form the logic board.