Please refer to SOM datasheet, for fan-header pinout details and to ensure the fan is connected correctly. There is no provision to control the FAN.
Also, when a question arises for control function of the fan, the SOM does not have provision to control the fan and the fan will run continuously when powered and cannot be regulated based on temperature or other conditions.
For further inquiries, please get in touch with mktg@iwave-global.com
Please find the detailed G40M product information in the below link,