In 2004 I completed a DEJ program and the case was dismissed. Why does my arrest show up on a pre-employment background check?

Whoever is running the background check on you is probably using the State's Dept of Justice Live Scan report. You can get a copy of your Live Scan report for yourself to see what is on it. (Google "Live Scan locations CA"). If there is erroneous info on your Live Scan report, there is a procedure for correcting the errors. But all arrests, criminal cases, and criminal case dispositions (including DEJ's, "expungements," and other "no-conviction" results will appear there permanently. That is not unlawful. The law addresses what use can be made of the info that appears there.

Unless you submitted fingerprints to your prospective employer , it is likely that a pre-employment back ground report contains your arrest information that was culled from public records of the county court where you were prosecuted. Ca dept of justice wrap sheets are confidential and would not be the source of a pre-employment background report (except if it was the type of position that you submitted fingerprints for)