Maybe a stupid question, bit what does the left brake lever do? mine goes all the way in, and does nothing i can notice...i have looked thru the manual, but no word about the function of this lever...

[2015 Z Force 800 53/Trail EPS]

One is just the front brakes and one is both front and rear. The one that goes all the way down must have air in it or is defective in some way.

Maybe a parking brake or a lever to the fot pedal. My guess is that it's a parking brake.

On the 600 EU model (think its called 550 in the US) the left handle is a parking brake. The right handle brakes both the front and rear discs, same with the right foot pedal on my CForce 600 EU model.