What indicates that your air brake system may have a leak?

Answer: D — All of the above

A leak in the air brake system can often be detected by various signs, which is why selecting all of the provided options is correct. An audible hissing sound is a common indicator of an air leak. This sound easily catches the driver's attention and suggests that air is escaping, which can severely impact the brake system's performance. Increased stopping distance can also be a sign of a leak. If air pressure is lower than optimal due to a leak, the brakes may not engage as effectively, leading to longer distances required to stop the vehicle. Lower air pressure than normal directly signals that there might be a leak in the system. Proper air pressure is crucial for the brakes to function effectively, and when it's diminished, it's often the result of air escaping from a compromised line or fitting. Thus, all of these indicators together point towards the possibility of an air brake system leak. Recognizing these signs promptly is essential for maintaining safety on the road.