What condition could cause the Reduced Performance light to illuminate in a Siemens train?

The illumination of the Reduced Performance light in a Siemens train typically indicates that a system is not functioning optimally, which can lead to a reduction in the train's operational capabilities. When the EP (Electro-Pneumatic) brake does not release, it creates a significant obstacle to the train's performance. This malfunction can cause the train to be unable to accelerate properly or maintain its desired speed, leading to a potential safety concern and a necessity to limit operation until the issue is resolved.

When the EP brake is engaged or fails to release, it directly impacts the traction and braking system, resulting in reduced power availability to the drive system. Therefore, this condition is a direct cause of the Reduced Performance light illuminating, as it signifies that the train may not be able to perform all functions as designed.

Other conditions, although they may affect performance, do not specifically reflect the immediate and critical nature of an EP brake that won't release. In contrast, the role of the EP brake is crucial for ensuring the train is able to operate effectively, making this option the correct choice regarding the trigger for the Reduced Performance light.