The „control ring“ is usually located at the left end of the handlebar. It controls the gear selection, the strength of the regenerative braking or the speed limit for cruise control, as well as the headlight.
The button ring's error statistics are unremarkable – there's little feedback regarding malfunctions.
In rare cases, one of the keys will fail, and a complete failure occurs slightly more often.
The solution to this error is usually not the control ring itself, but a connection problem with the Omni. The connection cable runs – sometimes with an additional plug connection – through the stem to the Omni and is connected to it via a JST connector.
If the control ring shows no function, check the cable connection and the corresponding JST slot in the Omni. How to remove the Omni is explained in the topic OMNI → „Expansion“.
Achtung: Buttonring ist nicht gleich Buttonring. Je nach Modell unterscheidet sich dieser in der Kabellänge und dem Anschlusstecker. Er ist als Einheit einzeln bestellbar, z.B. here.