What is the test for a motion to amend or amend a motor vehicle accident claim?

the nature of the claims are clear and no liability exists, or (b) it is probable from the nature of the defects and previous unsuccessful attempts to plead that the plaintiff cannot state a claim. [Citation.] [] . . . [T]he burden falls squarely on [the plaintiff] to show what facts [s]he could plead to state a cause of action if allowed the opportunity to replead. [Citation.] To meet this burden, a plaintiff must submit a proposed amended complaint or, on appeal, enumerate the facts and demonstrate how those facts establish a cause of action. [Citations.] Absent such a showing, the appellate court cannot assess whether or not the trial court abused its discretion by denying leave to amend." (Cantu v. Resolution Trust Corp. (1992) 4 Cal.App.4th 857, 889-890.)