The 2014 S1000R's 21F900 error number usually indicates an electrical system malfunction. This number may indicate a throttle position sensor or ECU issue.
Steps to troubleshoot:
Check Connections: Check throttle position sensor wiring and connectors for loose or broken connections.
Sometimes restarting the ECU fixes temporary issues. Remove the battery for a few minutes, then reconnect.
Dirt or residue might alter sensor readings, so check the throttle body.
Diagnostic kit: Read more detailed trouble codes and reset using a BMW motorbike diagnostic kit if feasible.
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Visit a technician: If the problem persists, take the bike to a skilled technician or BMW dealership for a diagnostic.