Chosen Solution
Left fan always shows 0 rpm in various fan control apps. After opening the bottom case, I see the left fan is clearly running idle at minimum, but won’t increase speed after maxing the speed through the app. Apple Diagnostics says there might be an issue with the fan. I’ve tried PRAM and SMC reset without success. What could be the issue? Damaged fan sensor or else? Many thanks, I. Arnold
The simple fix is to see if the fan its self has failed. There is two elements within the fan the motor part to spin the blades but there is also the feedback of a tachometer which tells the system what the fan is doing. I often find the tach’s die when the fan is running but not coming to speed and the monitoring app clearly shows zero or a very low RPM. Here’s the needed part MacBook Pro 15" Retina (Late 2013-Mid 2015) Left Fan as iFixit is out of stock here’s a second source Retina MacBook Pro 15" Fan - Left (13/14) Apple P/N 923-0669
I would look at Louis rossmann videos on YouTube here is one about fan speed https://youtu.be/3w4j_-JWrZs
