Is a confession involuntary if it was motivated by a promise of leniency or benefit to the accused?

A confession is involuntary if it was motivated by an express or implied promise of leniency or benefit to the accused. "However, mere advice or exhortation by the police that it would be better for the accused to tell the truth when unaccompanied by either a threat or a promise does not render a subsequent confession involuntary." (People v. Jimenez (1978) 21 Cal.3d 595, 611, overruled on other grounds in People v. Cahill (1993) 5 Cal.4th 478, 509-510, fn. 17.)