# Troubleshooting # Understanding the LEDS The lights on a Compute Module 4 (CM4), typically a **red Power (PWR) LED** and a **green Activity (ACT) LED**, indicate its operational status and can help diagnose boot problems. **LED Meanings** The behavior of the LEDs depends on the specific carrier board and software configuration, but generally follow these patterns: **Red Power (PWR) LED** - **Solid ON:** The CM4 board is receiving sufficient power (usually 5V or 12V, depending on the carrier board power input). - **OFF or Flickering:** Suspect a power supply issue. The power source may be faulty or not providing enough current. **Green Activity (ACT) LED** The green LED indicates the system's activity, particularly eMMC access, and can flash specific patterns to signal errors during the boot process. - **Flashing Irregularly:** Normal read/write activity is in progress, indicating the system is running or booting. - **Solid ON (after initial power-on):** The system has halted, and it's generally safe to power off the device. It may also be a sign of a non-booting state on some setups. - **Solid OFF:** The system may be off, or there might be an issue preventing it from accessing the boot media. - **Specific Flash Patterns:** These patterns diagnose early boot issues. For example: - **3 flashes:** start.elf (bootloader file) not found. - **4 flashes:** start.elf found but cannot be launched (potentially corrupted). - **7 flashes:** kernel.img not found. - **8 flashes:** SDRAM not recognized (may require a firmware update).