The Speedlite is not attached securely to the camera Attach the Speedlite's mounting foot securely to the camera The electrical contact of the Speedlite and the camera are dirty Clean the contact with a clean dry cloth If the Pilot light is red and is then pushed in and the Speedlite does not fire possibly The flash needs to be serviced
Custom Function Settings C.Fn-02-113: Convenient when you want to use the depth-of-field preview button to check the depth of field. C.Fn-08: If the Speedlite or camera's AF- assist beam is disabled, the AF- assist beam will not be emitted.