Which condition indicates a malfunction in the air brake system?

Answer: B — Unresponsive brake pedal

A brake pedal that is unresponsive is a clear indicator of a malfunction in the air brake system. This condition suggests that there may be a serious issue preventing the braking system from engaging properly. Potential causes could include air leaks, a failing brake compressor, or disrupted air pressure levels, all of which are critical components in the function of air brakes. In contrast, a steady driving speed can result from various factors, including proper functioning of the vehicle and its systems, so it does not indicate a brake malfunction. Increased fuel efficiency typically focuses on the engine and overall vehicle performance rather than directly reflecting the condition of the braking system. Flashing dashboard lights may indicate various problems but are not exclusively tied to brake failure; they could reference issues across multiple systems in the vehicle. Thus, an unresponsive brake pedal stands out as the most significant sign of a malfunction in the air brake system.