Auditing alter user commands

Hello everyone,

I am currently running Oracle 11.2.0.3 on Solaris 10.

I recently had a requirement to track the occurences of when a user alters his or her password. In this case, the user modifies his/her password via the alter user command, as opposed to other means. I issued the "alter user" command so that I can track the occurences, both success and failures. However, the audit logs appear to only show cases where an alter user command indeed was issued but a failure occured ie returncodes greater than 0.  For some reason, I do not see the succesfull occurences of the alter user statement ie returncodes equal to 0.