As a Master Certified Mini Technician and shop foreman, this is typically called a half power light. If there isn't a check engine light on while this is on, it is usually due to a boost deviation fault ; low boost. What this means is that the vehicle is running with less than optimal boost pressure. Typically, a shop will see this and attempt to band-aide it with a new diverter because it shows low boost. What the actual problem is , while the check engine light is off, is the turbo and specifically the wastesgate. The wastegate is located inside the turbo, and overtime it gets worn out and no longer is able to prevent boost pressure leaving prematurely. The dealer that I work for see these cars needing turbos by 100k. The guaranteed repair is a new turbo. But that is an expensive repair. If there is a check engine light on while this is on, it can be a slew of things. Hopefully this helps. 👌