What are the typical signs of a malfunctioning air brake system?

A malfunctioning air brake system can manifest in several critical ways, primarily through signs that indicate a loss of effective braking performance or system integrity. The presence of uneven braking, unusual noises, or a failure to stop is particularly alarming and indicates that there may be issues such as leaks in the brake lines, problems with the brake cylinders, or failure of the air compressor to maintain necessary pressure.

Uneven braking may present as one side of the vehicle experiencing less braking force than the other, leading to stability and control issues. Unusual noises, such as hissing, grinding, or knocking, can point to mechanical failures or air leaks within the system. A complete failure to stop suggests a serious malfunction, meaning that immediate inspection and repair are necessary to maintain safety.

The other options do not directly reflect the typical symptoms of air brake system malfunctions. Persistent vibrations during travel can arise from various mechanical issues but are not specific to air brakes. Increased fuel consumption and overheating of the engine relate more to powertrain and engine performance issues rather than the operation of the braking system. Therefore, the symptoms listed in the correct answer are directly related to the essential function and safety of the air brake system.