Which problem would cause a vibrating horn to sound in the Type 3 system?

In the context of the Type 3 system, a vibrating horn sounding is typically an indication of an alert or warning condition within the system. When a fuel pump fails, it can lead to significant issues such as a loss of pressure, potential contamination of the fuel system, or a failure to deliver fuel as needed. In response to such failures, warning systems are in place to notify operators of the problem. A vibrating horn serves as an audible alert to draw attention to the failure of the fuel pump, indicating that immediate action may be necessary to rectify the situation or prevent further complications.

In contrast, the conditions described in the other options may not necessarily trigger a vibrating horn. While an emergency stop button engaging may yield an alarm, it is typically a different type of signal such as a steady tone rather than a vibrating alert. Low or high high-level activation conditions in an operating storage tank may also have dedicated alarms but are not typically associated with pump failures, which tend to have a more pressing impact on system operation and safety.

Thus, the correct answer aligns with the system’s design to utilize a vibrating horn as a crucial response to critical operational issues, particularly related to fuel pump failures.