# What Do the LEDs Mean? The system LEDs are visible when mounted in a transparent enclosure and can also be used during system integration to help troubleshoot issues. The Ethernet LEDs are only active when connected to an Ethernet switch or host. The Ethernet Link Status LED comes on and stays on if a link is established. The Ethernet Activity LED flickers when Ethernet traffic is present. The Master Awake LED comes on and stays on if the master CPU starts booting (except as noted in the section on resetting the communications parameters). If it does not come on, it indicates issues with power, corrupted firmware, or failed CPU hardware. Issues with master firmware or hardware are not usually user-correctable but are also very uncommon. The Master Pinging LED comes on when the system has finished booting and flashes when the DVL is trying to operate. The Channel Awake LEDs come on and stay on when the channel CPUs boot. If they do not come on, it indicates issues with power, corrupted firmware, or failed CPU hardware. Unlike the master CPU, the channel CPUs can always be re-flashed as provided the master CPU is awake and able to talk to the Cerulean DVL console application. Issues with channel hardware are not usually user-correctable but are also very uncommon. The Channel Pinging LEDs come on when the system has finished booting and flashes when the DVL is trying to operate. ![Locations of system LEDs](/files/OzYtMRWWauvG3yw7uVDT) --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.ceruleansonar.com/c/dvl-75/communicating-with-the-dvl/what-do-the-leds-mean.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.