WHR-G54 Routers: Diag code key

Continuous Red:      On Startup.   RAM Error Red flash.

• Red Flash, 2 times:  On Startup.  Flash ROM Error
  
• Red Flash, 3 times:  On Startup.  A problem on the wired LAN Side
  
• Red Flash, 4 times: On Startup.  A problem on the wireless LAN Side
  

Also check:

• Power LED should be Green
  
• Wireless LED should be Green if the line is active. If it is blinking Green, wireless communication is active.
  
• Ethernet LED should be Green (100Mbps) or Amber (10Mbps) while the communication is active.
  
• The Red Diag LED will flash during boot and firmware updates.
  
• The Amber AOSS LED will glow while AOSS is in use.