A vehicle includes an engine, an air intake assembly having a variable geometry turbine (VGT) controllable using a turbine mass flow map, an exhaust manifold, and a controller. The controller calculates a pressure ratio between the inlet and outlet sides of the VGT, and first and second exhaust manifold pressures using respective first and second models. Each of the models extracts information from the map. The controller executes a control action using the first pressure when the ratio exceeds a threshold, using the second pressure otherwise. The controller itself is also disclosed herein, as is a method for controlling an engine operation aboard the vehicle. The method includes using the host machine to calculate the exhaust pressure ratio, to calculate the first and second pressures using the respective first and second models, and to execute a control action using the first or second exhaust pressure depending on the ratio.