This work, done in the framework of the French ANR DIAPASON2 project, investigates the possibility of evaluating the impact of the cathode stoichiometric ratio (FSC) on the local behavior of the PEMFC voltage signals. To this aim, the strength of the voltage local regularity is estimated using a nonlinear method based on the pointwise Hölder exponent (h): each voltage point is associated to an exponent value between 0 and 1. The analysis shows that the h exponent characterizes rigorously the FSC signatures on the stack and cell voltages. On the one hand, the h exponent decreases when reducing FSC from the nominal value (FSC=2). On the other hand, h increases for 23.5. The results obtained reflect the strong singularity of the voltages resulting from low and high FSC. The proposed method is a promising diagnostic tool to achieve on-line characterizations of PEMFC dynamical behaviors.