I use this as a reminder.

Cisco ASA - Allow Pinging of Outside Interface

Inbound ICMP through the PIX/ASA is denied by default. Outbound ICMP is permitted, but the incoming reply is denied by default. 

By default, you cannot ping the ASA’s outside interface - or in other words the public IP you assigned to it. To allow pinging of the outside interface:

ASA(config)#access-list ACL-OUTSIDE extended permit icmp any any 
ASA(config)#access-group ACL-OUTSIDE in interface outside