We present a method for automated engine calibration, by optimizing engine management settings and power-split control of a hybrid electric vehicle (HEV). The problem, which concerns minimization of fuel consumption under a NOxconstraint, is formulated as an optimal control problem. By applying Pontryagin's maximum principle, this paper shows that the problem is separable in space. In the case where the limits of battery state of charge are not activated, we show that the optimization problem is also separable in time. The optimal solution is obtained by iteratively solving the power-split control problem using dynamic programming or the equivalent consumption minimization strategy. In addition, we present a computationally efficient suboptimal solution, which aims at reducing the number of power-split optimizations required. An example is provided concerning optimization of engine management settings and power-split control of a parallel HEV.