Sleeping PowerBook

May 24th, 2007

My 15” PowerBook from April 2005 started going to sleep at random. Many people on the net are reporting similar problems. I traced the problem to a faulty temperature sensor beneath the track pad. The problem is faulty hardware which needs to be replaced, but you can apply a temporary software fix to prevent the temperature sensor from putting your PowerBook to sleep.

I have scheduled a repair for this PowerBook’s top case, which seems to be the only way to permanently resolve the issue. If your machine is still under Apple Care you should be able to take it to any Apple Store or AASP, who will replace the machine’s top case for free. This software workaround is not a permanent solution.

We need to disable the system’s response to the emergency temperature signal, which is shown in the system log as:


Power Management received emergency overtemp signal. Going to sleep.

You will be disabling a number of kernel extensions, which also manage other parts of the system’s functions. You might experience side effects that could very well negate the benefits of not having the PowerBook go to sleep at random. Overheating, or erratic power management, for example.

Here’s an overview of how to stop the emergency sleep sequence, with detailed explanation further down:

  1. Open a terminal window and make a new directory named kext.off.
  2. Move the thermal controller kernel extensions to this new directory.
  3. Remove the kernel extension caches.
  4. Reboot.

The kext.off directory will hold the disabled kernel extensions. This way, if you change your mind or need to replace them at any point, you’ll have them on hand to put back into place. Use Terminal.app to create the directory:


`sudo mkdir /kext.off`

Kernel extensions are stored in the /System/Library/Extensions/ directory. Move the following kernel extensions to the kext.off directory:


applelm7x.kext
applepmu.kext
ioi2ccontrollerpmu.kext
ioi2clm6x.kext
ioi2clm7x.kext
ioi2clm8x.kext

These kernel extensions control the thermal sensor beneath the track pad, the automatic shutdown sequences and a whole lot of others things I don’t know about. This pretty much lobotomizes the entire smart thermal system inside your PowerBook. You can verify this by downloading Temperature Monitor.

Be warned that this might have a negative impact on your PowerBook’s life span. Nevertheless, fans will still operate normally, and a number of other thermal sensors — including those monitoring the processor — will remain operational.

To make sure that Mac OS X loads a fresh set of kernel extensions after reboot you need to remove two cache files:


/System/Library/Extension.mcache
/System/Library/Extensions.mkext

After you’ve deleted those two file, reboot the system.

Did this work for you? Let me know if you have any other suggestions.