Solved Is The Sensor Reading The Fan Speed Located In The Fan Itself Macbook Pro 15 Unibody Late 2011

Chosen Solution

My left fan is working full speed (goes down to normal speed for few secs) . After lots of troubleshooting, I deduced that the computer is not able to read the proper RPM of the left fan (very low 0-200 RPM), hence it operates the fan at the highest speed as a fail-safe precaution. Now I am wondering, if this reading failure is stemming from a logic board issue or fan issue. So where is the sensor located? Is it in the fan itself or on the logic board? I ran AHT and it returned 4MOT/4/40000002 left side -0 I am asking to check if I am screwed or not :), and to decide whether to buy a new fan !!

UPDATE: Disconnecting the fan from the logic board and reconnecting it again solved the issue. The fan has been normal for a week now. I hope no one faces this issue, but if you do, try this before buying a new fan !!

You’ll need to replace the fan unit. The sensor is within the fan and not serviceable. Here’s the IFIXIT guide: MacBook Pro 15" Unibody Late 2011 Left Fan Replacement and heres the part you’ll need: Left Fan unit - Apple P/N 661-4952