Liability coverage pays what you owe other people. Uninsured motorist (UM) and underinsured motorist (UIM) coverage pays for your own injuries when the at-fault driver has no insurance or too little. An umbrella is liability coverage, so UM and UIM do not come along automatically.

The California rule: Insurance Code §11580.2(a)(1) excludes from the uninsured motorist requirement any policy whose auto liability coverage is provided only on an excess or umbrella basis. Underinsured motorist coverage is part of that same section. So the statute does not require an umbrella to carry UM or UIM. If an umbrella includes it, the coverage comes from the policy's own terms, such as an endorsement the insurer offers.

Because the section does not apply to umbrella-only policies, no signed deletion agreement is needed for the umbrella. The written agreement in §11580.2(a)(2) deletes coverage that the section would otherwise require. The primary auto policy is different: removing UM there does take a written agreement in the statutory form.

How UIM works on the primary policy: under §11580.2(p)(4), the most the UIM insurer owes is the insured's UIM limit minus the amount paid by or for the person legally liable. Example: a $250,000 UIM limit and an at-fault driver whose insurer pays $50,000 means at most $200,000 from the UIM coverage. An umbrella with no UM/UIM provision adds nothing to that claim.