A method of operating a front end accessory drive system for a motor vehicle, wherein the accessory drive system comprises one or more accessory components pulleys, e.g. air conditioner pulley 106, a motor generator pulley 102, a drive pulley 104, first and second idler pulleys 108, 110 and a flexible drive element, such as drive belt 112, configured to transmit a torque load between the one or more accessory components pulleys and the motor generator pulley. The method comprises determining a condition of the belt, determining a maximum permissible belt torque threshold, based on the determined condition of the belt. The method includes detecting an increase in torque demand on the belt, e.g. during a recuperation event, and determining when the torque demand on the belt will exceed the belt torque threshold. The method involves reducing the torque demand of one or more accessory components and/or a motor generator, so that the belt torque threshold is not exceeded and the belt will not experience parasitic losses such as belt slip and/or stretch etc.
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