You may notice the following message when attempting to connect to a database:
SQLSTATE[HY000]  Access denied for user 'db_user'@'localhost' (using password: YES)
This message typically indicates that the credentials used for the database user are incorrect. This type of message is typically a warning.
To determine if the credentials used are correct, please attempt to connect from the command line by typing the following:
mysql -u $db_user -p
Where $db_user is the actual database user.
If you are still unable to connect to MySQL with the specified database user, then chances are the password is incorrect. You can resolve the issue by resyncing the account's password. One way to reset the password is via WHM by going to:
Account Information » List Accounts
Once there, you will want to expand the information for the account by clicking on the plus sign.
You may also consider configuring the log_error_verbosity to 1, in which only error messages will display within the MySQL log file.
The following table shows the permitted values. The default is 3.
log_error_verbosity Value Permitted Messages
1 Error messages
2 Error and warning messages
3 Error, warning, and information messages