Is a liability insurer permitted to assume and conduct a defense of an action brought against the insured on the basis of forfeiture or noncoverage?

However, only liability insurers are subject to an exception. " 'The general rule supported by the great weight of authority is that if a liability insurer, with knowledge of a ground of forfeiture or noncoverage under the policy, assumes and conducts the defense of an action brought against the insured, without disclaiming liability and giving notice of its reservation of rights, it is thereafter precluded in an action upon the policy from setting up such ground of forfeiture or noncoverage. In other words, the insurer's unconditional defense of an action brought against the insured constitutes a waiver of the terms of the policy and an estoppel of the insured to assert such grounds.' [Citation.]" (Miller v. Elite Ins. Co. (1980) 100 Cal.App.3d 739, 755.)