My Mac’s fans are stuck on full blast!
Safe mode turns off third-party extensions, which should tell you if one of them is to blame
QMy iMac (27-inch, Mid 2010) started crashing when asleep, and now its internal fans are stuck blowing at full speed, even after resetting its SMC. What’s wrong with it?
AShut down your iMac, leave it to cool off for 10 minutes, then start it up in Apple Hardware Test (see apple.co/ 2b3FhpK for instructions on how to access that; you may need the install discs that came with your Mac). If that tool’s test results check out as normal and your Mac’s fans stay full on, reset the SMC and then its NVRAM (see the box below for instructions).
You may need to correct settings such as volume and display afterwards, but the fans should drop back to normal. If not, take your iMac to a Genius Bar for a complete check-up. Further crashes during sleep may disappear in safe mode (hold ß at the startup sound); this turns off third-party extensions, which should tell you if one of them is to blame.
Only one, TG Pro, gives you manual control over fans, which can sometimes help unstick their automatic control.
Several utilities such as System Monitor can provide useful information about internal temperatures and fan speeds.