Cal. Civ. Proc. Code § 999.4

(a) In any lawsuit filed by a claimant, or by a claimant as an assignee of the tortfeasor or by the tortfeasor for the benefit of the claimant, a time-limited demand that does not substantially comply with the terms of this chapter shall not be considered to be a reasonable offer to settle the claims against the tortfeasor for an amount within the insurance policy limits for purposes of any lawsuit alleging extracontractual damages against the tortfeasor’s liability insurer.
(b) This section shall not apply to a claimant that is not represented by counsel.
(c) In the event a court determines that this chapter conflicts with the Civil Discovery Act, (Title 4 (commencing with Section 2016.010) of Part 4), the Civil Discovery Act shall prevail.