Hello jgclark,
Welcome to the HP Forums! I hope you enjoy your stay!
I understand the computer displays a Cooling Fan 902 error, which is when the BIOS specifically detects an issue with the fan. I will do my best to assist you with this!
In regards to this specific computer, there is a special BIOS update which can resolve the issue. Please pick the correct BIOS which matches your computer model, located here: Error "Cooling Fan (902)" Appears when the Notebook is Powered On
If this BIOS update does not resolve the issue, the only other fault lies with the computer hardware. In this case, I will provide a document which suggests resetting the notebook and "properly" cleaning the system. This is the document to reference: System Fan (90b) error message on startup
Although the document is named for an error you do not witness, the troubleshooting steps are exactly the same. I believe trying everything above will resolve the issue.
If the issue is not resolved, I would contact HP phone support. The computer may need to be serviced to resolve the issue. You can utilize this website to learn how to contact HP appropriately, based on your region: Contact HP Worldwide
I hope you find this information helpful. Please let me know if you have any other questions or concerns. Thanks for bringing this issue to the HP Forums. Have a great day!
Mario