Cal. Fam. Code § 4003

In any case in which the support of a child is at issue, the court may, upon a showing of good cause, order a separate trial on that issue. The separate trial shall be given preference over other civil cases, except matters to which special precedence may be given by law, for assigning a trial date. If the court has also ordered a separate trial on the issue of custody pursuant to Section 3023, the two issues shall be tried together.