The Mac Pro logic board includes a set of LEDs to help troubleshoot the
computer. The LEDs are located toward the rear of the logic board, under the memory cage, next
to PCI card slot 1. You can view these LEDs by removing the computer’s side access panel and
looking through the memory cage to the logic board below. LEDs 2, 3, 4, and 5 are normally off
and will automatically illuminate if an error occurs. To read LEDs 1, 6, 7, and 8, you must press the
DIAG_LED button, which is adjacent to the LEDs. To press the DIAG_LED button, use the nylon
probe tool.
Location Name Color Nominal Press DIAG_LED button to displayIndicates
Led 1 Trickle Pwr Yellow On Yes Power supply is providing trickle power
Led 2 CPU B Error Red Off No CPU B halts on an IERR(instructionerror)
Led 3 CPU A Error Red Off No CPU A halts on an IERR(instructionerror)
Led 4 CPU B OT Red Off No CPU B is over temperature
Led 5 CPU A OT Red Off No CPU A is over temperature
Led 6 GPU Present Green On Yes EFI has configuredthe graphicscard
Led 7 Power On Green On Yes All power rails are functioning
Led 8 EFI Done Green On Yes EFI is done loading
