Can a defendant withdraw a guilty plea under section 1018 of the Criminal Code?

To the extent defendant is attempting to withdraw his plea because it is invalid due to his lack of understanding, such claim fails. Section 1018 provides, in relevant part: "On application of the defendant at any time before judgment or within six months after an order granting probation is made if entry of judgment is suspended, the court may, and in case of a defendant who appeared without counsel at the time of the plea the court shall, for a good cause shown, permit the plea of guilty to be withdrawn and a plea of not guilty substituted." "Mistake, ignorance or any other factor overcoming the exercise of free judgment is good cause for withdrawal of a guilty plea. [Citations.] But good cause must be shown by clear and convincing evidence." (People v. Cruz (1974) 12 Cal.3d 562, 566.)