POST Code 99 - Super I/O Initialization

What is POST-CODE-99?

POST Code 99 - Super I/O Initialization ranks as a high-severity motherboard issue in our database. Motherboard debug code 99 indicates a failure during Super I/O chip initialization, which handles legacy hardware connections, front panel ports, and display outputs. Most commonly caused by loose display cables, graphics card seating issues, or conflicting USB devices. This can also stem from corrupt BIOS settings or outdated firmware. Use the steps below to track down and fix the cause.

Common Causes

• Incorrect display output connection or cable
• Graphics card not fully seated in the PCIe slot
• Conflicting external USB or SATA storage devices
• Corrupt BIOS settings or outdated firmware

Step-by-Step Fix Guide

• 1
  Ensure display cable is plugged into the discrete GPU, not motherboard

  The highest-success first step is Ensure display cable is plugged into the discrete GPU, which targets the most common trigger behind POST-CODE-99.

• 2
  Reseat the graphics card in the primary PCIe x16 slot

  If the problem isn't fully resolved yet, the remaining steps rule out the less frequent motherboard instability triggers.

• 3
  Unplug all non-essential USB devices and restart

  "Unplug all non-essential USB devices and restart" is worth trying when conflicting external USB or SATA storage devices turns out to be the culprit.

• 4
  Perform a CMOS reset to clear hardware mapping

  "Perform a CMOS reset to clear hardware mapping" handles an edge case some users report with POST-CODE-99.

Commands & Diagnostics

Frequently Asked Questions