An engine control system of a vehicle comprises a reserves module and a fault diagnostic module. The reserves module controls airflow into an engine based on a driver torque request, increases the airflow into the engine when a reserve torque request is received, and outputs a torque output command for the engine based on the driver torque request. The fault diagnostic module selectively diagnoses a fault in the reserves module when the torque output command is greater than a sum of the driver torque request, a predetermined torque, and a load applied to the engine.