What is indicated by the failure of the compressor?

The failure of the compressor typically leads to the illumination of a maintenance fault light. This light serves as a warning indicator to alert operators or maintenance personnel that there is an issue that needs to be addressed. The compressor is a critical component for many train systems, particularly for air brake systems and other pneumatic operations. When the compressor fails, it can disrupt the normal functioning of the entire system and indicate that maintenance is required, which is why the fault light becomes essential for safety and operational integrity.

The other choices reference operational states or mechanisms that do not directly correlate with the specific indication of a compressor failure; therefore they would not accurately represent the consequence of such a failure.