The answer has several aspects.

The rental car rented on a short term basis is considered a nonowned auto under the terms of the physical damage section of the PAP. The other sources of recovery clause under the PAP's physical damage section declares that any insurance provided with respect to a nonowned auto shall be excess over any other collectible source of recovery. This other collectible source includes any coverage provided by the owner of the nonowned auto. So, if the rental car vendor has physical damage coverage for the car rented by the insured, the insured's PAP will provide excess coverage.

Consider also that, as regards insurance for a nonowned auto, the other sources of recovery clause describes as a collectible source “any other source of recovery applicable to the loss”. This takes into account if an insured is not liable for the damage. For example, if the insured were hit by an at-fault driver, the insured's auto policy will provide excess physical damage coverage if the at-fault driver provides a collectible source of recovery. If the at-fault driver has liability insurance or can pay for the damage out of pocket, that is a source of recovery applicable to the loss.

The rental contract may state that the renter is solely responsible for any damage to the rented car. The renter's PAP declares that it is excess over any other collectible source of recovery. If the rental company does not provide any other collectible source of recovery for the damage to the rented car, that makes the renter's PAP primary. So, if the rental company does not provide physical damage coverage or if the insured is hit by an unknown or uninsured driver, there is no other collectible source of recovery and the renter's auto policy drops down into the primary role.

Finally, note that the current PAP contains an exclusion that blocks coverage for loss to or loss of use of a nonowned car rented to the named insured if a rental company is precluded from recovering such loss from the named insured pursuant to the provisions of any rental agreement or state law. If that is the case, this means the renter's PAP will not respond to the loss and the question of primary or excess coverage is irrelevant.