Method of estimating catalyst temperature of a multi-displacement internal combustion engine

A method of estimating temperature of a catalyst associated with a cylinder bank of a multi-displacement internal combustion engine having multiple cylinder banks associated with multiple catalysts. A temperature estimate of the catalysts associated with the multiple cylinder banks is set substantially equal to a base model temperature. Deactivation of a cylinder bank of the multiple cylinder banks is determined, and a catalyst cooldown correction is identified for the catalyst associated with the deactivated cylinder bank from a catalyst cooldown model including time elapsed since deactivation of the cylinder bank. The catalyst cooldown correction is applied to the temperature estimate of the catalyst associated with the deactivated cylinder bank to update the temperature estimate of the catalyst.