S.C. Code § 38-77-160
Automobile insurance carriers shall offer, at the option of the insured, uninsured motorist coverage up to the limits of the insured's liability coverage in addition to the mandatory coverage prescribed by Section 38-77-150. Such carriers shall also offer, at the option of the insured, underinsured motorist coverage up to the limits of the insured liability coverage to provide coverage in the event that damages are sustained in excess of the liability limits carried by an at-fault insured or underinsured motorist or in excess of any damages cap or limitation imposed by statute. If, however, an insured or named insured is protected by uninsured or underinsured motorist coverage in excess of the basic limits, the policy shall provide that the insured or named insured is protected only to the extent of the coverage he has on the vehicle involved in the accident. If none of the insured's or named insured's vehicles is involved in the accident, coverage is available only to the extent of coverage on any one of the vehicles with the excess or underinsured coverage. Benefits paid pursuant to this section are not subject to subrogation and assignment.
No action may be brought under the underinsured motorist provision unless copies of the pleadings in the action establishing liability are served in the manner provided by law upon the insurer writing the underinsured motorist provision. The insurer has the right to appear and defend in the name of the underinsured motorist in any action which may affect its liability and has thirty days after service of process on it in which to appear. The evidence of service upon the insurer may not be made a part of the record. In the event the automobile insurance insurer for the putative at-fault insured chooses to settle in part the claims against its insured by payment of its applicable liability limits on behalf of its insured, the underinsured motorist insurer may assume control of the defense of action for its own benefit. No underinsured motorist policy may contain a clause requiring the insurer's consent to settlement with the at-fault party.
S.C. Code § 38-77-160