CA Fam Code Section 7648.3

A court may not issue an order setting aside or vacating a judgment establishing paternity pursuant to this article under any of the following circumstances:

(a)

The judgment was made or entered by a tribunal of another state, even if the enforcement of that judgment is sought in this state.

(b)

The judgment was made or entered in this state and genetic tests were conducted prior to the entry of the judgment which did not exclude the previously established father as the biological father of the child.