Calculations are performed for purely vibrational inelasticity in proton–CO collisions at energies below 1 eV. A realistic spherical potential and an approximate stretching parameter for the coupling matrix elements between target states are introduced. The appearance of Feshbach-type, core-excited resonances are studied for both the collinear and 3 D situation. The n=0→1 inelastic cross section energy dependence is studied between the first and second thresholds of an harmonic oscillator target description. A strong dependence on the coupling matrix is found for the resonance structures and widths, while an ultrasimple evaluation of perturbative corrections for locating the resonance positions is also discussed. A clustering and broadening of the resonances are found in this system and indicate that experimental detection in the low energy collisional regime may be possible.