!
error HP
Error Code 9 blinks, 1 blink every second followed by a 2 second pause
Bad option card.
? What Causes This
Incorrect or damaged expansion cards.
✓ How to Fix It
Identify and remove faulty expansion cards. If the issue persists, it could be a system board problem, consult support.
Source: page 2 of the official manual
From the manual
This error code appears in:
HP Elitedesk 800 G1 Small Form Factor PC